Update bundled copy of pexpect to 3.3

Closes gh-6086

IPython/external/pexpect/_pexpect.py

@@ -1,2044 +1,2123
 '''Pexpect is a Python module for spawning child applications and controlling
 them automatically. Pexpect can be used for automating interactive applications
 such as ssh, ftp, passwd, telnet, etc. It can be used to a automate setup
 scripts for duplicating software package installations on different servers. It
 can be used for automated software testing. Pexpect is in the spirit of Don
 Libes' Expect, but Pexpect is pure Python. Other Expect-like modules for Python
 require TCL and Expect or require C extensions to be compiled. Pexpect does not
 use C, Expect, or TCL extensions. It should work on any platform that supports
 the standard Python pty module. The Pexpect interface focuses on ease of use so
 that simple tasks are easy.
 
 There are two main interfaces to the Pexpect system; these are the function,
 run() and the class, spawn. The spawn class is more powerful. The run()
 function is simpler than spawn, and is good for quickly calling program. When
 you call the run() function it executes a given program and then returns the
 output. This is a handy replacement for os.system().
 
 For example::
 
     pexpect.run('ls -la')
 
 The spawn class is the more powerful interface to the Pexpect system. You can
 use this to spawn a child program then interact with it by sending input and
 expecting responses (waiting for patterns in the child's output).
 
 For example::
 
     child = pexpect.spawn('scp foo [e-mail]:.')
     child.expect('Password:')
     child.sendline(mypassword)
 
 This works even for commands that ask for passwords or other input outside of
 the normal stdio streams. For example, ssh reads input directly from the TTY
 device which bypasses stdin.
 
 Credits: Noah Spurrier, Richard Holden, Marco Molteni, Kimberley Burchett,
 Robert Stone, Hartmut Goebel, Chad Schroeder, Erick Tryzelaar, Dave Kirby, Ids
 vander Molen, George Todd, Noel Taylor, Nicolas D. Cesar, Alexander Gattin,
 Jacques-Etienne Baudoux, Geoffrey Marshall, Francisco Lourenco, Glen Mabey,
 Karthik Gurusamy, Fernando Perez, Corey Minyard, Jon Cohen, Guillaume
 Chazarain, Andrew Ryan, Nick Craig-Wood, Andrew Stone, Jorgen Grahn, John
 Spiegel, Jan Grant, and Shane Kerr. Let me know if I forgot anyone.
 
 Pexpect is free, open source, and all that good stuff.
 http://pexpect.sourceforge.net/
 
 PEXPECT LICENSE
 
     This license is approved by the OSI and FSF as GPL-compatible.
         http://opensource.org/licenses/isc-license.txt
 
     Copyright (c) 2012, Noah Spurrier <[e-mail]>
     PERMISSION TO USE, COPY, MODIFY, AND/OR DISTRIBUTE THIS SOFTWARE FOR ANY
     PURPOSE WITH OR WITHOUT FEE IS HEREBY GRANTED, PROVIDED THAT THE ABOVE
     COPYRIGHT NOTICE AND THIS PERMISSION NOTICE APPEAR IN ALL COPIES.
     THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
     WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
     ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
     ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
     OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 '''
 
 try:
     import os
     import sys
     import time
     import select
     import re
     import struct
     import resource
     import types
     import pty
     import tty
     import termios
     import fcntl
     import errno
     import traceback
     import signal
     import codecs
+    import stat
 except ImportError:  # pragma: no cover
     err = sys.exc_info()[1]
     raise ImportError(str(err) + '''
 
 A critical module was not found. Probably this operating system does not
 support it. Pexpect is intended for UNIX-like operating systems.''')
 
-__version__ = '3.2'
+__version__ = '3.3'
 __revision__ = ''
 __all__ = ['ExceptionPexpect', 'EOF', 'TIMEOUT', 'spawn', 'spawnu', 'run', 'runu',
            'which', 'split_command_line', '__version__', '__revision__']
 
 PY3 = (sys.version_info[0] >= 3)
 
 # Exception classes used by this module.
 class ExceptionPexpect(Exception):
     '''Base class for all exceptions raised by this module.
     '''
 
     def __init__(self, value):
         super(ExceptionPexpect, self).__init__(value)
         self.value = value
 
     def __str__(self):
         return str(self.value)
 
     def get_trace(self):
         '''This returns an abbreviated stack trace with lines that only concern
         the caller. In other words, the stack trace inside the Pexpect module
         is not included. '''
 
         tblist = traceback.extract_tb(sys.exc_info()[2])
         tblist = [item for item in tblist if 'pexpect/__init__' not in item[0]]
         tblist = traceback.format_list(tblist)
         return ''.join(tblist)
 
 
 class EOF(ExceptionPexpect):
     '''Raised when EOF is read from a child.
     This usually means the child has exited.'''
 
 
 class TIMEOUT(ExceptionPexpect):
     '''Raised when a read time exceeds the timeout. '''
 
 ##class TIMEOUT_PATTERN(TIMEOUT):
 ##    '''Raised when the pattern match time exceeds the timeout.
 ##    This is different than a read TIMEOUT because the child process may
 ##    give output, thus never give a TIMEOUT, but the output
 ##    may never match a pattern.
 ##    '''
 ##class MAXBUFFER(ExceptionPexpect):
 ##    '''Raised when a buffer fills before matching an expected pattern.'''
 
 
 def run(command, timeout=-1, withexitstatus=False, events=None,
         extra_args=None, logfile=None, cwd=None, env=None):
 
     '''
     This function runs the given command; waits for it to finish; then
     returns all output as a string. STDERR is included in output. If the full
     path to the command is not given then the path is searched.
 
     Note that lines are terminated by CR/LF (\\r\\n) combination even on
     UNIX-like systems because this is the standard for pseudottys. If you set
     'withexitstatus' to true, then run will return a tuple of (command_output,
     exitstatus). If 'withexitstatus' is false then this returns just
     command_output.
 
     The run() function can often be used instead of creating a spawn instance.
     For example, the following code uses spawn::
 
         from pexpect import *
         child = spawn('scp foo [e-mail]:.')
         child.expect('(?i)password')
         child.sendline(mypassword)
 
     The previous code can be replace with the following::
 
         from pexpect import *
         run('scp foo [e-mail]:.', events={'(?i)password': mypassword})
 
     **Examples**
 
     Start the apache daemon on the local machine::
 
         from pexpect import *
         run("/usr/local/apache/bin/apachectl start")
 
     Check in a file using SVN::
 
         from pexpect import *
         run("svn ci -m 'automatic commit' my_file.py")
 
     Run a command and capture exit status::
 
         from pexpect import *
         (command_output, exitstatus) = run('ls -l /bin', withexitstatus=1)
 
     The following will run SSH and execute 'ls -l' on the remote machine. The
     password 'secret' will be sent if the '(?i)password' pattern is ever seen::
 
         run("ssh [e-mail] 'ls -l'",
             events={'(?i)password':'secret\\n'})
 
     This will start mencoder to rip a video from DVD. This will also display
     progress ticks every 5 seconds as it runs. For example::
 
         from pexpect import *
         def print_ticks(d):
             print d['event_count'],
         run("mencoder dvd://1 -o video.avi -oac copy -ovc copy",
             events={TIMEOUT:print_ticks}, timeout=5)
 
     The 'events' argument should be a dictionary of patterns and responses.
     Whenever one of the patterns is seen in the command out run() will send the
     associated response string. Note that you should put newlines in your
     string if Enter is necessary. The responses may also contain callback
     functions. Any callback is function that takes a dictionary as an argument.
     The dictionary contains all the locals from the run() function, so you can
     access the child spawn object or any other variable defined in run()
     (event_count, child, and extra_args are the most useful). A callback may
     return True to stop the current run process otherwise run() continues until
     the next event. A callback may also return a string which will be sent to
     the child. 'extra_args' is not used by directly run(). It provides a way to
     pass data to a callback function through run() through the locals
     dictionary passed to a callback.
     '''
     return _run(command, timeout=timeout, withexitstatus=withexitstatus,
                 events=events, extra_args=extra_args, logfile=logfile, cwd=cwd,
                 env=env, _spawn=spawn)
 
 def runu(command, timeout=-1, withexitstatus=False, events=None,
         extra_args=None, logfile=None, cwd=None, env=None, **kwargs):
     """This offers the same interface as :func:`run`, but using unicode.
 
     Like :class:`spawnu`, you can pass ``encoding`` and ``errors`` parameters,
     which will be used for both input and output.
     """
     return _run(command, timeout=timeout, withexitstatus=withexitstatus,
                 events=events, extra_args=extra_args, logfile=logfile, cwd=cwd,
                 env=env, _spawn=spawnu, **kwargs)
 
 def _run(command, timeout, withexitstatus, events, extra_args, logfile, cwd,
          env, _spawn, **kwargs):
     if timeout == -1:
         child = _spawn(command, maxread=2000, logfile=logfile, cwd=cwd, env=env,
                         **kwargs)
     else:
         child = _spawn(command, timeout=timeout, maxread=2000, logfile=logfile,
                 cwd=cwd, env=env, **kwargs)
     if events is not None:
         patterns = list(events.keys())
         responses = list(events.values())
     else:
         # This assumes EOF or TIMEOUT will eventually cause run to terminate.
         patterns = None
         responses = None
     child_result_list = []
     event_count = 0
     while True:
         try:
             index = child.expect(patterns)
             if isinstance(child.after, child.allowed_string_types):
                 child_result_list.append(child.before + child.after)
             else:
                 # child.after may have been a TIMEOUT or EOF,
                 # which we don't want appended to the list.
                 child_result_list.append(child.before)
             if isinstance(responses[index], child.allowed_string_types):
                 child.send(responses[index])
             elif isinstance(responses[index], types.FunctionType):
                 callback_result = responses[index](locals())
                 sys.stdout.flush()
                 if isinstance(callback_result, child.allowed_string_types):
                     child.send(callback_result)
                 elif callback_result:
                     break
             else:
                 raise TypeError('The callback must be a string or function.')
             event_count = event_count + 1
         except TIMEOUT:
             child_result_list.append(child.before)
             break
         except EOF:
             child_result_list.append(child.before)
             break
     child_result = child.string_type().join(child_result_list)
     if withexitstatus:
         child.close()
         return (child_result, child.exitstatus)
     else:
         return child_result
 
 class spawn(object):
     '''This is the main class interface for Pexpect. Use this class to start
     and control child applications. '''
     string_type = bytes
     if PY3:
         allowed_string_types = (bytes, str)
         @staticmethod
         def _chr(c):
             return bytes([c])
         linesep = os.linesep.encode('ascii')
+        crlf = '\r\n'.encode('ascii')
 
         @staticmethod
         def write_to_stdout(b):
             try:
                 return sys.stdout.buffer.write(b)
             except AttributeError:
                 # If stdout has been replaced, it may not have .buffer
                 return sys.stdout.write(b.decode('ascii', 'replace'))
     else:
         allowed_string_types = (basestring,)  # analysis:ignore
         _chr = staticmethod(chr)
         linesep = os.linesep
+        crlf = '\r\n'
         write_to_stdout = sys.stdout.write
 
     encoding = None
 
     def __init__(self, command, args=[], timeout=30, maxread=2000,
         searchwindowsize=None, logfile=None, cwd=None, env=None,
-        ignore_sighup=True):
+        ignore_sighup=True, echo=True):
 
         '''This is the constructor. The command parameter may be a string that
         includes a command and any arguments to the command. For example::
 
             child = pexpect.spawn('/usr/bin/ftp')
             child = pexpect.spawn('/usr/bin/ssh [e-mail]')
             child = pexpect.spawn('ls -latr /tmp')
 
         You may also construct it with a list of arguments like so::
 
             child = pexpect.spawn('/usr/bin/ftp', [])
             child = pexpect.spawn('/usr/bin/ssh', ['[e-mail]'])
             child = pexpect.spawn('ls', ['-latr', '/tmp'])
 
         After this the child application will be created and will be ready to
         talk to. For normal use, see expect() and send() and sendline().
 
         Remember that Pexpect does NOT interpret shell meta characters such as
         redirect, pipe, or wild cards (``>``, ``|``, or ``*``). This is a
         common mistake.  If you want to run a command and pipe it through
         another command then you must also start a shell. For example::
 
             child = pexpect.spawn('/bin/bash -c "ls -l | grep LOG > logs.txt"')
             child.expect(pexpect.EOF)
 
         The second form of spawn (where you pass a list of arguments) is useful
         in situations where you wish to spawn a command and pass it its own
         argument list. This can make syntax more clear. For example, the
         following is equivalent to the previous example::
 
             shell_cmd = 'ls -l | grep LOG > logs.txt'
             child = pexpect.spawn('/bin/bash', ['-c', shell_cmd])
             child.expect(pexpect.EOF)
 
         The maxread attribute sets the read buffer size. This is maximum number
         of bytes that Pexpect will try to read from a TTY at one time. Setting
         the maxread size to 1 will turn off buffering. Setting the maxread
         value higher may help performance in cases where large amounts of
         output are read back from the child. This feature is useful in
         conjunction with searchwindowsize.
 
         The searchwindowsize attribute sets the how far back in the incoming
         seach buffer Pexpect will search for pattern matches. Every time
         Pexpect reads some data from the child it will append the data to the
         incoming buffer. The default is to search from the beginning of the
         incoming buffer each time new data is read from the child. But this is
         very inefficient if you are running a command that generates a large
         amount of data where you want to match. The searchwindowsize does not
         affect the size of the incoming data buffer. You will still have
         access to the full buffer after expect() returns.
 
         The logfile member turns on or off logging. All input and output will
         be copied to the given file object. Set logfile to None to stop
         logging. This is the default. Set logfile to sys.stdout to echo
         everything to standard output. The logfile is flushed after each write.
 
         Example log input and output to a file::
 
             child = pexpect.spawn('some_command')
             fout = file('mylog.txt','w')
             child.logfile = fout
 
         Example log to stdout::
 
             child = pexpect.spawn('some_command')
             child.logfile = sys.stdout
 
         The logfile_read and logfile_send members can be used to separately log
         the input from the child and output sent to the child. Sometimes you
         don't want to see everything you write to the child. You only want to
         log what the child sends back. For example::
 
             child = pexpect.spawn('some_command')
             child.logfile_read = sys.stdout
 
         To separately log output sent to the child use logfile_send::
 
             self.logfile_send = fout
 
         If ``ignore_sighup`` is True, the child process will ignore SIGHUP
         signals. For now, the default is True, to preserve the behaviour of
         earlier versions of Pexpect, but you should pass this explicitly if you
         want to rely on it.
 
         The delaybeforesend helps overcome a weird behavior that many users
         were experiencing. The typical problem was that a user would expect() a
         "Password:" prompt and then immediately call sendline() to send the
         password. The user would then see that their password was echoed back
         to them. Passwords don't normally echo. The problem is caused by the
         fact that most applications print out the "Password" prompt and then
         turn off stdin echo, but if you send your password before the
         application turned off echo, then you get your password echoed.
         Normally this wouldn't be a problem when interacting with a human at a
         real keyboard. If you introduce a slight delay just before writing then
         this seems to clear up the problem. This was such a common problem for
         many users that I decided that the default pexpect behavior should be
         to sleep just before writing to the child application. 1/20th of a
         second (50 ms) seems to be enough to clear up the problem. You can set
         delaybeforesend to 0 to return to the old behavior. Most Linux machines
         don't like this to be below 0.03. I don't know why.
 
         Note that spawn is clever about finding commands on your path.
         It uses the same logic that "which" uses to find executables.
 
         If you wish to get the exit status of the child you must call the
         close() method. The exit or signal status of the child will be stored
         in self.exitstatus or self.signalstatus. If the child exited normally
         then exitstatus will store the exit return code and signalstatus will
         be None. If the child was terminated abnormally with a signal then
         signalstatus will store the signal value and exitstatus will be None.
         If you need more detail you can also read the self.status member which
         stores the status returned by os.waitpid. You can interpret this using
-        os.WIFEXITED/os.WEXITSTATUS or os.WIFSIGNALED/os.TERMSIG. '''
+        os.WIFEXITED/os.WEXITSTATUS or os.WIFSIGNALED/os.TERMSIG.
+
+        The echo attribute may be set to False to disable echoing of input.
+        As a pseudo-terminal, all input echoed by the "keyboard" (send()
+        or sendline()) will be repeated to output.  For many cases, it is
+        not desirable to have echo enabled, and it may be later disabled
+        using setecho(False) followed by waitnoecho().  However, for some
+        platforms such as Solaris, this is not possible, and should be
+        disabled immediately on spawn.
+        '''
 
         self.STDIN_FILENO = pty.STDIN_FILENO
         self.STDOUT_FILENO = pty.STDOUT_FILENO
         self.STDERR_FILENO = pty.STDERR_FILENO
         self.stdin = sys.stdin
         self.stdout = sys.stdout
         self.stderr = sys.stderr
 
         self.searcher = None
         self.ignorecase = False
         self.before = None
         self.after = None
         self.match = None
         self.match_index = None
         self.terminated = True
         self.exitstatus = None
         self.signalstatus = None
         # status returned by os.waitpid
         self.status = None
         self.flag_eof = False
         self.pid = None
-        # the chile filedescriptor is initially closed
+        # the child file descriptor is initially closed
         self.child_fd = -1
         self.timeout = timeout
         self.delimiter = EOF
         self.logfile = logfile
         # input from child (read_nonblocking)
         self.logfile_read = None
         # output to send (send, sendline)
         self.logfile_send = None
         # max bytes to read at one time into buffer
         self.maxread = maxread
         # This is the read buffer. See maxread.
         self.buffer = self.string_type()
         # Data before searchwindowsize point is preserved, but not searched.
         self.searchwindowsize = searchwindowsize
         # Delay used before sending data to child. Time in seconds.
         # Most Linux machines don't like this to be below 0.03 (30 ms).
         self.delaybeforesend = 0.05
         # Used by close() to give kernel time to update process status.
         # Time in seconds.
         self.delayafterclose = 0.1
         # Used by terminate() to give kernel time to update process status.
         # Time in seconds.
         self.delayafterterminate = 0.1
         self.softspace = False
         self.name = '<' + repr(self) + '>'
         self.closed = True
         self.cwd = cwd
         self.env = env
+        self.echo = echo
         self.ignore_sighup = ignore_sighup
+        _platform = sys.platform.lower()
         # This flags if we are running on irix
-        self.__irix_hack = (sys.platform.lower().find('irix') >= 0)
+        self.__irix_hack = _platform.startswith('irix')
         # Solaris uses internal __fork_pty(). All others use pty.fork().
-        if ((sys.platform.lower().find('solaris') >= 0)
-            or (sys.platform.lower().find('sunos5') >= 0)):
-            self.use_native_pty_fork = False
-        else:
-            self.use_native_pty_fork = True
-
+        self.use_native_pty_fork = not (
+                _platform.startswith('solaris') or
+                _platform.startswith('sunos'))
+        # inherit EOF and INTR definitions from controlling process.
+        try:
+            from termios import VEOF, VINTR
+            fd = sys.__stdin__.fileno()
+            self._INTR = ord(termios.tcgetattr(fd)[6][VINTR])
+            self._EOF = ord(termios.tcgetattr(fd)[6][VEOF])
+        except (ImportError, OSError, IOError, termios.error):
+            # unless the controlling process is also not a terminal,
+            # such as cron(1). Fall-back to using CEOF and CINTR.
+            try:
+                from termios import CEOF, CINTR
+                (self._INTR, self._EOF) = (CINTR, CEOF)
+            except ImportError:
+                #                         ^C, ^D
+                (self._INTR, self._EOF) = (3, 4)
         # Support subclasses that do not use command or args.
         if command is None:
             self.command = None
             self.args = None
             self.name = '<pexpect factory incomplete>'
         else:
             self._spawn(command, args)
 
     @staticmethod
     def _coerce_expect_string(s):
         if not isinstance(s, bytes):
             return s.encode('ascii')
         return s
 
     @staticmethod
     def _coerce_send_string(s):
         if not isinstance(s, bytes):
             return s.encode('utf-8')
         return s
 
     @staticmethod
     def _coerce_read_string(s):
         return s
 
     def __del__(self):
         '''This makes sure that no system resources are left open. Python only
         garbage collects Python objects. OS file descriptors are not Python
         objects, so they must be handled explicitly. If the child file
         descriptor was opened outside of this class (passed to the constructor)
         then this does not close it. '''
 
         if not self.closed:
             # It is possible for __del__ methods to execute during the
             # teardown of the Python VM itself. Thus self.close() may
             # trigger an exception because os.close may be None.
             try:
                 self.close()
             # which exception, shouldnt' we catch explicitly .. ?
             except:
                 pass
 
     def __str__(self):
         '''This returns a human-readable string that represents the state of
         the object. '''
 
         s = []
         s.append(repr(self))
         s.append('version: ' + __version__)
         s.append('command: ' + str(self.command))
         s.append('args: %r' % (self.args,))
         s.append('searcher: %r' % (self.searcher,))
         s.append('buffer (last 100 chars): %r' % (self.buffer)[-100:],)
         s.append('before (last 100 chars): %r' % (self.before)[-100:],)
         s.append('after: %r' % (self.after,))
         s.append('match: %r' % (self.match,))
         s.append('match_index: ' + str(self.match_index))
         s.append('exitstatus: ' + str(self.exitstatus))
         s.append('flag_eof: ' + str(self.flag_eof))
         s.append('pid: ' + str(self.pid))
         s.append('child_fd: ' + str(self.child_fd))
         s.append('closed: ' + str(self.closed))
         s.append('timeout: ' + str(self.timeout))
         s.append('delimiter: ' + str(self.delimiter))
         s.append('logfile: ' + str(self.logfile))
         s.append('logfile_read: ' + str(self.logfile_read))
         s.append('logfile_send: ' + str(self.logfile_send))
         s.append('maxread: ' + str(self.maxread))
         s.append('ignorecase: ' + str(self.ignorecase))
         s.append('searchwindowsize: ' + str(self.searchwindowsize))
         s.append('delaybeforesend: ' + str(self.delaybeforesend))
         s.append('delayafterclose: ' + str(self.delayafterclose))
         s.append('delayafterterminate: ' + str(self.delayafterterminate))
         return '\n'.join(s)
 
     def _spawn(self, command, args=[]):
         '''This starts the given command in a child process. This does all the
         fork/exec type of stuff for a pty. This is called by __init__. If args
         is empty then command will be parsed (split on spaces) and args will be
         set to parsed arguments. '''
 
         # The pid and child_fd of this object get set by this method.
         # Note that it is difficult for this method to fail.
         # You cannot detect if the child process cannot start.
         # So the only way you can tell if the child process started
         # or not is to try to read from the file descriptor. If you get
         # EOF immediately then it means that the child is already dead.
         # That may not necessarily be bad because you may have spawned a child
         # that performs some task; creates no stdout output; and then dies.
 
         # If command is an int type then it may represent a file descriptor.
         if isinstance(command, type(0)):
             raise ExceptionPexpect('Command is an int type. ' +
                     'If this is a file descriptor then maybe you want to ' +
                     'use fdpexpect.fdspawn which takes an existing ' +
                     'file descriptor instead of a command string.')
 
         if not isinstance(args, type([])):
             raise TypeError('The argument, args, must be a list.')
 
         if args == []:
             self.args = split_command_line(command)
             self.command = self.args[0]
         else:
             # Make a shallow copy of the args list.
             self.args = args[:]
             self.args.insert(0, command)
             self.command = command
 
         command_with_path = which(self.command)
         if command_with_path is None:
             raise ExceptionPexpect('The command was not found or was not ' +
                     'executable: %s.' % self.command)
         self.command = command_with_path
         self.args[0] = self.command
 
         self.name = '<' + ' '.join(self.args) + '>'
 
         assert self.pid is None, 'The pid member must be None.'
         assert self.command is not None, 'The command member must not be None.'
 
         if self.use_native_pty_fork:
             try:
                 self.pid, self.child_fd = pty.fork()
-            except OSError:
+            except OSError:  # pragma: no cover
                 err = sys.exc_info()[1]
                 raise ExceptionPexpect('pty.fork() failed: ' + str(err))
         else:
             # Use internal __fork_pty
             self.pid, self.child_fd = self.__fork_pty()
 
-        if self.pid == 0:
+        # Some platforms must call setwinsize() and setecho() from the
+        # child process, and others from the master process. We do both,
+        # allowing IOError for either.
+
+        if self.pid == pty.CHILD:
             # Child
+            self.child_fd = self.STDIN_FILENO
+
+            # set default window size of 24 rows by 80 columns
             try:
-                # used by setwinsize()
-                self.child_fd = sys.stdout.fileno()
                 self.setwinsize(24, 80)
-            # which exception, shouldnt' we catch explicitly .. ?
-            except:
-                # Some platforms do not like setwinsize (Cygwin).
-                # This will cause problem when running applications that
-                # are very picky about window size.
-                # This is a serious limitation, but not a show stopper.
-                pass
+            except IOError as err:
+                if err.args[0] not in (errno.EINVAL, errno.ENOTTY):
+                    raise
+
+            # disable echo if spawn argument echo was unset
+            if not self.echo:
+                try:
+                    self.setecho(self.echo)
+                except (IOError, termios.error) as err:
+                    if err.args[0] not in (errno.EINVAL, errno.ENOTTY):
+                        raise
+
             # Do not allow child to inherit open file descriptors from parent.
             max_fd = resource.getrlimit(resource.RLIMIT_NOFILE)[0]
-            for i in range(3, max_fd):
-                try:
-                    os.close(i)
-                except OSError:
-                    pass
+            os.closerange(3, max_fd)
 
             if self.ignore_sighup:
                 signal.signal(signal.SIGHUP, signal.SIG_IGN)
 
             if self.cwd is not None:
                 os.chdir(self.cwd)
             if self.env is None:
                 os.execv(self.command, self.args)
             else:
                 os.execvpe(self.command, self.args, self.env)
 
         # Parent
+        try:
+            self.setwinsize(24, 80)
+        except IOError as err:
+            if err.args[0] not in (errno.EINVAL, errno.ENOTTY):
+                raise
+
+
         self.terminated = False
         self.closed = False
 
     def __fork_pty(self):
         '''This implements a substitute for the forkpty system call. This
         should be more portable than the pty.fork() function. Specifically,
         this should work on Solaris.
 
         Modified 10.06.05 by Geoff Marshall: Implemented __fork_pty() method to
         resolve the issue with Python's pty.fork() not supporting Solaris,
         particularly ssh. Based on patch to posixmodule.c authored by Noah
         Spurrier::
 
             http://mail.python.org/pipermail/python-dev/2003-May/035281.html
 
         '''
 
         parent_fd, child_fd = os.openpty()
         if parent_fd < 0 or child_fd < 0:
             raise ExceptionPexpect("Could not open with os.openpty().")
 
         pid = os.fork()
-        if pid < 0:
-            raise ExceptionPexpect("Failed os.fork().")
-        elif pid == 0:
+        if pid == pty.CHILD:
             # Child.
             os.close(parent_fd)
             self.__pty_make_controlling_tty(child_fd)
 
-            os.dup2(child_fd, 0)
-            os.dup2(child_fd, 1)
-            os.dup2(child_fd, 2)
+            os.dup2(child_fd, self.STDIN_FILENO)
+            os.dup2(child_fd, self.STDOUT_FILENO)
+            os.dup2(child_fd, self.STDERR_FILENO)
 
-            if child_fd > 2:
-                os.close(child_fd)
         else:
             # Parent.
             os.close(child_fd)
 
         return pid, parent_fd
 
     def __pty_make_controlling_tty(self, tty_fd):
         '''This makes the pseudo-terminal the controlling tty. This should be
         more portable than the pty.fork() function. Specifically, this should
         work on Solaris. '''
 
         child_name = os.ttyname(tty_fd)
 
-        # Disconnect from controlling tty. Harmless if not already connected.
+        # Disconnect from controlling tty, if any.  Raises OSError of ENXIO
+        # if there was no controlling tty to begin with, such as when
+        # executed by a cron(1) job.
         try:
             fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
-            if fd >= 0:
                 os.close(fd)
-        # which exception, shouldnt' we catch explicitly .. ?
-        except:
-            # Already disconnected. This happens if running inside cron.
-            pass
+        except OSError as err:
+            if err.errno != errno.ENXIO:
+                raise
 
         os.setsid()
 
-        # Verify we are disconnected from controlling tty
-        # by attempting to open it again.
+        # Verify we are disconnected from controlling tty by attempting to open
+        # it again.  We expect that OSError of ENXIO should always be raised.
         try:
             fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
-            if fd >= 0:
                 os.close(fd)
-                raise ExceptionPexpect('Failed to disconnect from ' +
-                    'controlling tty. It is still possible to open /dev/tty.')
-        # which exception, shouldnt' we catch explicitly .. ?
-        except:
-            # Good! We are disconnected from a controlling tty.
-            pass
+            raise ExceptionPexpect("OSError of errno.ENXIO should be raised.")
+        except OSError as err:
+            if err.errno != errno.ENXIO:
+                raise
 
         # Verify we can open child pty.
         fd = os.open(child_name, os.O_RDWR)
-        if fd < 0:
-            raise ExceptionPexpect("Could not open child pty, " + child_name)
-        else:
             os.close(fd)
 
         # Verify we now have a controlling tty.
         fd = os.open("/dev/tty", os.O_WRONLY)
-        if fd < 0:
-            raise ExceptionPexpect("Could not open controlling tty, /dev/tty")
-        else:
             os.close(fd)
 
+
     def fileno(self):
         '''This returns the file descriptor of the pty for the child.
         '''
         return self.child_fd
 
     def close(self, force=True):
         '''This closes the connection with the child application. Note that
         calling close() more than once is valid. This emulates standard Python
         behavior with files. Set force to True if you want to make sure that
         the child is terminated (SIGKILL is sent if the child ignores SIGHUP
         and SIGINT). '''
 
         if not self.closed:
             self.flush()
             os.close(self.child_fd)
             # Give kernel time to update process status.
             time.sleep(self.delayafterclose)
             if self.isalive():
                 if not self.terminate(force):
                     raise ExceptionPexpect('Could not terminate the child.')
             self.child_fd = -1
             self.closed = True
             #self.pid = None
 
     def flush(self):
         '''This does nothing. It is here to support the interface for a
         File-like object. '''
 
         pass
 
     def isatty(self):
         '''This returns True if the file descriptor is open and connected to a
-        tty(-like) device, else False. '''
+        tty(-like) device, else False.
+
+        On SVR4-style platforms implementing streams, such as SunOS and HP-UX,
+        the child pty may not appear as a terminal device.  This means
+        methods such as setecho(), setwinsize(), getwinsize() may raise an
+        IOError. '''
 
         return os.isatty(self.child_fd)
 
     def waitnoecho(self, timeout=-1):
         '''This waits until the terminal ECHO flag is set False. This returns
         True if the echo mode is off. This returns False if the ECHO flag was
         not set False before the timeout. This can be used to detect when the
         child is waiting for a password. Usually a child application will turn
         off echo mode when it is waiting for the user to enter a password. For
         example, instead of expecting the "password:" prompt you can wait for
         the child to set ECHO off::
 
             p = pexpect.spawn('ssh [e-mail]')
             p.waitnoecho()
             p.sendline(mypassword)
 
         If timeout==-1 then this method will use the value in self.timeout.
         If timeout==None then this method to block until ECHO flag is False.
         '''
 
         if timeout == -1:
             timeout = self.timeout
         if timeout is not None:
             end_time = time.time() + timeout
         while True:
             if not self.getecho():
                 return True
             if timeout < 0 and timeout is not None:
                 return False
             if timeout is not None:
                 timeout = end_time - time.time()
             time.sleep(0.1)
 
     def getecho(self):
         '''This returns the terminal echo mode. This returns True if echo is
         on or False if echo is off. Child applications that are expecting you
-        to enter a password often set ECHO False. See waitnoecho(). '''
+        to enter a password often set ECHO False. See waitnoecho().
+
+        Not supported on platforms where ``isatty()`` returns False.  '''
 
+        try:
         attr = termios.tcgetattr(self.child_fd)
-        if attr[3] & termios.ECHO:
-            return True
-        return False
+        except termios.error as err:
+            errmsg = 'getecho() may not be called on this platform'
+            if err.args[0] == errno.EINVAL:
+                raise IOError(err.args[0], '%s: %s.' % (err.args[1], errmsg))
+            raise
+
+        self.echo = bool(attr[3] & termios.ECHO)
+        return self.echo
 
     def setecho(self, state):
         '''This sets the terminal echo mode on or off. Note that anything the
         child sent before the echo will be lost, so you should be sure that
         your input buffer is empty before you call setecho(). For example, the
         following will work as expected::
 
             p = pexpect.spawn('cat') # Echo is on by default.
             p.sendline('1234') # We expect see this twice from the child...
             p.expect(['1234']) # ... once from the tty echo...
             p.expect(['1234']) # ... and again from cat itself.
             p.setecho(False) # Turn off tty echo
             p.sendline('abcd') # We will set this only once (echoed by cat).
             p.sendline('wxyz') # We will set this only once (echoed by cat)
             p.expect(['abcd'])
             p.expect(['wxyz'])
 
         The following WILL NOT WORK because the lines sent before the setecho
         will be lost::
 
             p = pexpect.spawn('cat')
             p.sendline('1234')
             p.setecho(False) # Turn off tty echo
             p.sendline('abcd') # We will set this only once (echoed by cat).
             p.sendline('wxyz') # We will set this only once (echoed by cat)
             p.expect(['1234'])
             p.expect(['1234'])
             p.expect(['abcd'])
             p.expect(['wxyz'])
+
+
+        Not supported on platforms where ``isatty()`` returns False.
         '''
 
-        self.child_fd
+        errmsg = 'setecho() may not be called on this platform'
+
+        try:
         attr = termios.tcgetattr(self.child_fd)
+        except termios.error as err:
+            if err.args[0] == errno.EINVAL:
+                raise IOError(err.args[0], '%s: %s.' % (err.args[1], errmsg))
+            raise
+
         if state:
             attr[3] = attr[3] | termios.ECHO
         else:
             attr[3] = attr[3] & ~termios.ECHO
-        # I tried TCSADRAIN and TCSAFLUSH, but
-        # these were inconsistent and blocked on some platforms.
-        # TCSADRAIN would probably be ideal if it worked.
+
+        try:
+            # I tried TCSADRAIN and TCSAFLUSH, but these were inconsistent and
+            # blocked on some platforms. TCSADRAIN would probably be ideal.
         termios.tcsetattr(self.child_fd, termios.TCSANOW, attr)
+        except IOError as err:
+            if err.args[0] == errno.EINVAL:
+                raise IOError(err.args[0], '%s: %s.' % (err.args[1], errmsg))
+            raise
+
+        self.echo = state
 
     def _log(self, s, direction):
         if self.logfile is not None:
             self.logfile.write(s)
             self.logfile.flush()
         second_log = self.logfile_send if (direction=='send') else self.logfile_read
         if second_log is not None:
             second_log.write(s)
             second_log.flush()
 
     def read_nonblocking(self, size=1, timeout=-1):
         '''This reads at most size characters from the child application. It
         includes a timeout. If the read does not complete within the timeout
         period then a TIMEOUT exception is raised. If the end of file is read
         then an EOF exception will be raised. If a log file was set using
         setlog() then all data will also be written to the log file.
 
         If timeout is None then the read may block indefinitely.
         If timeout is -1 then the self.timeout value is used. If timeout is 0
         then the child is polled and if there is no data immediately ready
         then this will raise a TIMEOUT exception.
 
         The timeout refers only to the amount of time to read at least one
         character. This is not effected by the 'size' parameter, so if you call
         read_nonblocking(size=100, timeout=30) and only one character is
         available right away then one character will be returned immediately.
         It will not wait for 30 seconds for another 99 characters to come in.
 
         This is a wrapper around os.read(). It uses select.select() to
         implement the timeout. '''
 
         if self.closed:
             raise ValueError('I/O operation on closed file.')
 
         if timeout == -1:
             timeout = self.timeout
 
         # Note that some systems such as Solaris do not give an EOF when
         # the child dies. In fact, you can still try to read
         # from the child_fd -- it will block forever or until TIMEOUT.
         # For this case, I test isalive() before doing any reading.
         # If isalive() is false, then I pretend that this is the same as EOF.
         if not self.isalive():
             # timeout of 0 means "poll"
             r, w, e = self.__select([self.child_fd], [], [], 0)
             if not r:
                 self.flag_eof = True
                 raise EOF('End Of File (EOF). Braindead platform.')
         elif self.__irix_hack:
             # Irix takes a long time before it realizes a child was terminated.
             # FIXME So does this mean Irix systems are forced to always have
             # FIXME a 2 second delay when calling read_nonblocking? That sucks.
             r, w, e = self.__select([self.child_fd], [], [], 2)
             if not r and not self.isalive():
                 self.flag_eof = True
                 raise EOF('End Of File (EOF). Slow platform.')
 
         r, w, e = self.__select([self.child_fd], [], [], timeout)
 
         if not r:
             if not self.isalive():
                 # Some platforms, such as Irix, will claim that their
                 # processes are alive; timeout on the select; and
                 # then finally admit that they are not alive.
                 self.flag_eof = True
                 raise EOF('End of File (EOF). Very slow platform.')
             else:
                 raise TIMEOUT('Timeout exceeded.')
 
         if self.child_fd in r:
             try:
                 s = os.read(self.child_fd, size)
-            except OSError:
-                # Linux does this
+            except OSError as err:
+                if err.args[0] == errno.EIO:
+                    # Linux-style EOF
                 self.flag_eof = True
                 raise EOF('End Of File (EOF). Exception style platform.')
+                raise
             if s == b'':
-                # BSD style
+                # BSD-style EOF
                 self.flag_eof = True
                 raise EOF('End Of File (EOF). Empty string style platform.')
 
             s = self._coerce_read_string(s)
             self._log(s, 'read')
             return s
 
-        raise ExceptionPexpect('Reached an unexpected state.')
+        raise ExceptionPexpect('Reached an unexpected state.')  # pragma: no cover
 
     def read(self, size=-1):
         '''This reads at most "size" bytes from the file (less if the read hits
         EOF before obtaining size bytes). If the size argument is negative or
         omitted, read all data until EOF is reached. The bytes are returned as
         a string object. An empty string is returned when EOF is encountered
         immediately. '''
 
         if size == 0:
             return self.string_type()
         if size < 0:
             # delimiter default is EOF
             self.expect(self.delimiter)
             return self.before
 
         # I could have done this more directly by not using expect(), but
         # I deliberately decided to couple read() to expect() so that
         # I would catch any bugs early and ensure consistant behavior.
         # It's a little less efficient, but there is less for me to
         # worry about if I have to later modify read() or expect().
         # Note, it's OK if size==-1 in the regex. That just means it
         # will never match anything in which case we stop only on EOF.
         cre = re.compile(self._coerce_expect_string('.{%d}' % size), re.DOTALL)
         # delimiter default is EOF
         index = self.expect([cre, self.delimiter])
         if index == 0:
             ### FIXME self.before should be ''. Should I assert this?
             return self.after
         return self.before
 
     def readline(self, size=-1):
         '''This reads and returns one entire line. The newline at the end of
         line is returned as part of the string, unless the file ends without a
         newline. An empty string is returned if EOF is encountered immediately.
         This looks for a newline as a CR/LF pair (\\r\\n) even on UNIX because
         this is what the pseudotty device returns. So contrary to what you may
         expect you will receive newlines as \\r\\n.
 
         If the size argument is 0 then an empty string is returned. In all
         other cases the size argument is ignored, which is not standard
         behavior for a file-like object. '''
 
         if size == 0:
             return self.string_type()
         # delimiter default is EOF
-        index = self.expect([b'\r\n', self.delimiter])
+        index = self.expect([self.crlf, self.delimiter])
         if index == 0:
-            return self.before + b'\r\n'
+            return self.before + self.crlf
         else:
             return self.before
 
     def __iter__(self):
         '''This is to support iterators over a file-like object.
         '''
         return iter(self.readline, self.string_type())
 
     def readlines(self, sizehint=-1):
         '''This reads until EOF using readline() and returns a list containing
         the lines thus read. The optional 'sizehint' argument is ignored.
         Remember, because this reads until EOF that means the child
         process should have closed its stdout. If you run this method on
         a child that is still running with its stdout open then this
         method will block until it timesout.'''
 
         lines = []
         while True:
             line = self.readline()
             if not line:
                 break
             lines.append(line)
         return lines
 
     def write(self, s):
         '''This is similar to send() except that there is no return value.
         '''
 
         self.send(s)
 
     def writelines(self, sequence):
         '''This calls write() for each element in the sequence. The sequence
         can be any iterable object producing strings, typically a list of
         strings. This does not add line separators. There is no return value.
         '''
 
         for s in sequence:
             self.write(s)
 
     def send(self, s):
         '''Sends string ``s`` to the child process, returning the number of
         bytes written. If a logfile is specified, a copy is written to that
         log. '''
 
         time.sleep(self.delaybeforesend)
 
         s = self._coerce_send_string(s)
         self._log(s, 'send')
 
         return self._send(s)
 
     def _send(self, s):
         return os.write(self.child_fd, s)
 
     def sendline(self, s=''):
         '''Wraps send(), sending string ``s`` to child process, with os.linesep
         automatically appended. Returns number of bytes written. '''
 
         n = self.send(s)
         n = n + self.send(self.linesep)
         return n
 
     def sendcontrol(self, char):
 
         '''Helper method that wraps send() with mnemonic access for sending control
         character to the child (such as Ctrl-C or Ctrl-D).  For example, to send
         Ctrl-G (ASCII 7, bell, '\a')::
 
             child.sendcontrol('g')
 
         See also, sendintr() and sendeof().
         '''
 
         char = char.lower()
         a = ord(char)
         if a >= 97 and a <= 122:
             a = a - ord('a') + 1
             return self.send(self._chr(a))
         d = {'@': 0, '`': 0,
             '[': 27, '{': 27,
             '\\': 28, '|': 28,
             ']': 29, '}': 29,
             '^': 30, '~': 30,
             '_': 31,
             '?': 127}
         if char not in d:
             return 0
         return self.send(self._chr(d[char]))
 
     def sendeof(self):
 
         '''This sends an EOF to the child. This sends a character which causes
         the pending parent output buffer to be sent to the waiting child
         program without waiting for end-of-line. If it is the first character
         of the line, the read() in the user program returns 0, which signifies
         end-of-file. This means to work as expected a sendeof() has to be
         called at the beginning of a line. This method does not send a newline.
         It is the responsibility of the caller to ensure the eof is sent at the
         beginning of a line. '''
 
-        ### Hmmm... how do I send an EOF?
-        ###C  if ((m = write(pty, *buf, p - *buf)) < 0)
-        ###C      return (errno == EWOULDBLOCK) ? n : -1;
-        #fd = sys.stdin.fileno()
-        #old = termios.tcgetattr(fd) # remember current state
-        #attr = termios.tcgetattr(fd)
-        #attr[3] = attr[3] | termios.ICANON # ICANON must be set to see EOF
-        #try: # use try/finally to ensure state gets restored
-        #    termios.tcsetattr(fd, termios.TCSADRAIN, attr)
-        #    if hasattr(termios, 'CEOF'):
-        #        os.write(self.child_fd, '%c' % termios.CEOF)
-        #    else:
-        #        # Silly platform does not define CEOF so assume CTRL-D
-        #        os.write(self.child_fd, '%c' % 4)
-        #finally: # restore state
-        #    termios.tcsetattr(fd, termios.TCSADRAIN, old)
-        if hasattr(termios, 'VEOF'):
-            char = ord(termios.tcgetattr(self.child_fd)[6][termios.VEOF])
-        else:
-            # platform does not define VEOF so assume CTRL-D
-            char = 4
-        self.send(self._chr(char))
+        self.send(self._chr(self._EOF))
 
     def sendintr(self):
 
         '''This sends a SIGINT to the child. It does not require
         the SIGINT to be the first character on a line. '''
 
-        if hasattr(termios, 'VINTR'):
-            char = ord(termios.tcgetattr(self.child_fd)[6][termios.VINTR])
-        else:
-            # platform does not define VINTR so assume CTRL-C
-            char = 3
-        self.send(self._chr(char))
+        self.send(self._chr(self._INTR))
 
     def eof(self):
 
         '''This returns True if the EOF exception was ever raised.
         '''
 
         return self.flag_eof
 
     def terminate(self, force=False):
 
         '''This forces a child process to terminate. It starts nicely with
         SIGHUP and SIGINT. If "force" is True then moves onto SIGKILL. This
         returns True if the child was terminated. This returns False if the
         child could not be terminated. '''
 
         if not self.isalive():
             return True
         try:
             self.kill(signal.SIGHUP)
             time.sleep(self.delayafterterminate)
             if not self.isalive():
                 return True
             self.kill(signal.SIGCONT)
             time.sleep(self.delayafterterminate)
             if not self.isalive():
                 return True
             self.kill(signal.SIGINT)
             time.sleep(self.delayafterterminate)
             if not self.isalive():
                 return True
             if force:
                 self.kill(signal.SIGKILL)
                 time.sleep(self.delayafterterminate)
                 if not self.isalive():
                     return True
                 else:
                     return False
             return False
         except OSError:
             # I think there are kernel timing issues that sometimes cause
             # this to happen. I think isalive() reports True, but the
             # process is dead to the kernel.
             # Make one last attempt to see if the kernel is up to date.
             time.sleep(self.delayafterterminate)
             if not self.isalive():
                 return True
             else:
                 return False
 
     def wait(self):
 
         '''This waits until the child exits. This is a blocking call. This will
         not read any data from the child, so this will block forever if the
         child has unread output and has terminated. In other words, the child
         may have printed output then called exit(), but, the child is
         technically still alive until its output is read by the parent. '''
 
         if self.isalive():
             pid, status = os.waitpid(self.pid, 0)
         else:
             raise ExceptionPexpect('Cannot wait for dead child process.')
         self.exitstatus = os.WEXITSTATUS(status)
         if os.WIFEXITED(status):
             self.status = status
             self.exitstatus = os.WEXITSTATUS(status)
             self.signalstatus = None
             self.terminated = True
         elif os.WIFSIGNALED(status):
             self.status = status
             self.exitstatus = None
             self.signalstatus = os.WTERMSIG(status)
             self.terminated = True
-        elif os.WIFSTOPPED(status):
+        elif os.WIFSTOPPED(status):  # pragma: no cover
             # You can't call wait() on a child process in the stopped state.
             raise ExceptionPexpect('Called wait() on a stopped child ' +
                     'process. This is not supported. Is some other ' +
                     'process attempting job control with our child pid?')
         return self.exitstatus
 
     def isalive(self):
 
         '''This tests if the child process is running or not. This is
         non-blocking. If the child was terminated then this will read the
         exitstatus or signalstatus of the child. This returns True if the child
         process appears to be running or False if not. It can take literally
         SECONDS for Solaris to return the right status. '''
 
         if self.terminated:
             return False
 
         if self.flag_eof:
             # This is for Linux, which requires the blocking form
-            # of waitpid to # get status of a defunct process.
+            # of waitpid to get the status of a defunct process.
             # This is super-lame. The flag_eof would have been set
             # in read_nonblocking(), so this should be safe.
             waitpid_options = 0
         else:
             waitpid_options = os.WNOHANG
 
         try:
             pid, status = os.waitpid(self.pid, waitpid_options)
         except OSError:
             err = sys.exc_info()[1]
             # No child processes
             if err.errno == errno.ECHILD:
                 raise ExceptionPexpect('isalive() encountered condition ' +
                         'where "terminated" is 0, but there was no child ' +
                         'process. Did someone else call waitpid() ' +
                         'on our process?')
             else:
                 raise err
 
         # I have to do this twice for Solaris.
         # I can't even believe that I figured this out...
         # If waitpid() returns 0 it means that no child process
         # wishes to report, and the value of status is undefined.
         if pid == 0:
             try:
                 ### os.WNOHANG) # Solaris!
                 pid, status = os.waitpid(self.pid, waitpid_options)
-            except OSError as e:
+            except OSError as e:  # pragma: no cover
                 # This should never happen...
                 if e.errno == errno.ECHILD:
                     raise ExceptionPexpect('isalive() encountered condition ' +
                             'that should never happen. There was no child ' +
                             'process. Did someone else call waitpid() ' +
                             'on our process?')
                 else:
                     raise
 
             # If pid is still 0 after two calls to waitpid() then the process
             # really is alive. This seems to work on all platforms, except for
             # Irix which seems to require a blocking call on waitpid or select,
             # so I let read_nonblocking take care of this situation
             # (unfortunately, this requires waiting through the timeout).
             if pid == 0:
                 return True
 
         if pid == 0:
             return True
 
         if os.WIFEXITED(status):
             self.status = status
             self.exitstatus = os.WEXITSTATUS(status)
             self.signalstatus = None
             self.terminated = True
         elif os.WIFSIGNALED(status):
             self.status = status
             self.exitstatus = None
             self.signalstatus = os.WTERMSIG(status)
             self.terminated = True
         elif os.WIFSTOPPED(status):
             raise ExceptionPexpect('isalive() encountered condition ' +
                     'where child process is stopped. This is not ' +
                     'supported. Is some other process attempting ' +
                     'job control with our child pid?')
         return False
 
     def kill(self, sig):
 
         '''This sends the given signal to the child application. In keeping
         with UNIX tradition it has a misleading name. It does not necessarily
         kill the child unless you send the right signal. '''
 
         # Same as os.kill, but the pid is given for you.
         if self.isalive():
             os.kill(self.pid, sig)
 
     def _pattern_type_err(self, pattern):
         raise TypeError('got {badtype} ({badobj!r}) as pattern, must be one'
                         ' of: {goodtypes}, pexpect.EOF, pexpect.TIMEOUT'\
                         .format(badtype=type(pattern),
                                 badobj=pattern,
                                 goodtypes=', '.join([str(ast)\
                                     for ast in self.allowed_string_types])
                                 )
                         )
 
     def compile_pattern_list(self, patterns):
 
         '''This compiles a pattern-string or a list of pattern-strings.
         Patterns must be a StringType, EOF, TIMEOUT, SRE_Pattern, or a list of
         those. Patterns may also be None which results in an empty list (you
         might do this if waiting for an EOF or TIMEOUT condition without
         expecting any pattern).
 
         This is used by expect() when calling expect_list(). Thus expect() is
         nothing more than::
 
              cpl = self.compile_pattern_list(pl)
              return self.expect_list(cpl, timeout)
 
         If you are using expect() within a loop it may be more
         efficient to compile the patterns first and then call expect_list().
         This avoid calls in a loop to compile_pattern_list()::
 
              cpl = self.compile_pattern_list(my_pattern)
              while some_condition:
                 ...
                 i = self.expect_list(clp, timeout)
                 ...
         '''
 
         if patterns is None:
             return []
         if not isinstance(patterns, list):
             patterns = [patterns]
 
         # Allow dot to match \n
         compile_flags = re.DOTALL
         if self.ignorecase:
             compile_flags = compile_flags | re.IGNORECASE
         compiled_pattern_list = []
         for idx, p in enumerate(patterns):
             if isinstance(p, self.allowed_string_types):
                 p = self._coerce_expect_string(p)
                 compiled_pattern_list.append(re.compile(p, compile_flags))
             elif p is EOF:
                 compiled_pattern_list.append(EOF)
             elif p is TIMEOUT:
                 compiled_pattern_list.append(TIMEOUT)
             elif isinstance(p, type(re.compile(''))):
                 compiled_pattern_list.append(p)
             else:
                 self._pattern_type_err(p)
         return compiled_pattern_list
 
     def expect(self, pattern, timeout=-1, searchwindowsize=-1):
 
         '''This seeks through the stream until a pattern is matched. The
         pattern is overloaded and may take several types. The pattern can be a
         StringType, EOF, a compiled re, or a list of any of those types.
         Strings will be compiled to re types. This returns the index into the
         pattern list. If the pattern was not a list this returns index 0 on a
         successful match. This may raise exceptions for EOF or TIMEOUT. To
         avoid the EOF or TIMEOUT exceptions add EOF or TIMEOUT to the pattern
         list. That will cause expect to match an EOF or TIMEOUT condition
         instead of raising an exception.
 
         If you pass a list of patterns and more than one matches, the first
         match in the stream is chosen. If more than one pattern matches at that
         point, the leftmost in the pattern list is chosen. For example::
 
             # the input is 'foobar'
             index = p.expect(['bar', 'foo', 'foobar'])
             # returns 1('foo') even though 'foobar' is a "better" match
 
         Please note, however, that buffering can affect this behavior, since
         input arrives in unpredictable chunks. For example::
 
             # the input is 'foobar'
             index = p.expect(['foobar', 'foo'])
             # returns 0('foobar') if all input is available at once,
             # but returs 1('foo') if parts of the final 'bar' arrive late
 
         After a match is found the instance attributes 'before', 'after' and
         'match' will be set. You can see all the data read before the match in
         'before'. You can see the data that was matched in 'after'. The
         re.MatchObject used in the re match will be in 'match'. If an error
         occurred then 'before' will be set to all the data read so far and
         'after' and 'match' will be None.
 
         If timeout is -1 then timeout will be set to the self.timeout value.
 
         A list entry may be EOF or TIMEOUT instead of a string. This will
         catch these exceptions and return the index of the list entry instead
         of raising the exception. The attribute 'after' will be set to the
         exception type. The attribute 'match' will be None. This allows you to
         write code like this::
 
                 index = p.expect(['good', 'bad', pexpect.EOF, pexpect.TIMEOUT])
                 if index == 0:
                     do_something()
                 elif index == 1:
                     do_something_else()
                 elif index == 2:
                     do_some_other_thing()
                 elif index == 3:
                     do_something_completely_different()
 
         instead of code like this::
 
                 try:
                     index = p.expect(['good', 'bad'])
                     if index == 0:
                         do_something()
                     elif index == 1:
                         do_something_else()
                 except EOF:
                     do_some_other_thing()
                 except TIMEOUT:
                     do_something_completely_different()
 
         These two forms are equivalent. It all depends on what you want. You
         can also just expect the EOF if you are waiting for all output of a
         child to finish. For example::
 
                 p = pexpect.spawn('/bin/ls')
                 p.expect(pexpect.EOF)
                 print p.before
 
         If you are trying to optimize for speed then see expect_list().
         '''
 
         compiled_pattern_list = self.compile_pattern_list(pattern)
         return self.expect_list(compiled_pattern_list,
                 timeout, searchwindowsize)
 
     def expect_list(self, pattern_list, timeout=-1, searchwindowsize=-1):
 
         '''This takes a list of compiled regular expressions and returns the
         index into the pattern_list that matched the child output. The list may
         also contain EOF or TIMEOUT(which are not compiled regular
         expressions). This method is similar to the expect() method except that
         expect_list() does not recompile the pattern list on every call. This
         may help if you are trying to optimize for speed, otherwise just use
         the expect() method.  This is called by expect(). If timeout==-1 then
         the self.timeout value is used. If searchwindowsize==-1 then the
         self.searchwindowsize value is used. '''
 
         return self.expect_loop(searcher_re(pattern_list),
                 timeout, searchwindowsize)
 
     def expect_exact(self, pattern_list, timeout=-1, searchwindowsize=-1):
 
         '''This is similar to expect(), but uses plain string matching instead
         of compiled regular expressions in 'pattern_list'. The 'pattern_list'
         may be a string; a list or other sequence of strings; or TIMEOUT and
         EOF.
 
         This call might be faster than expect() for two reasons: string
         searching is faster than RE matching and it is possible to limit the
         search to just the end of the input buffer.
 
         This method is also useful when you don't want to have to worry about
         escaping regular expression characters that you want to match.'''
 
         if (isinstance(pattern_list, self.allowed_string_types) or
                 pattern_list in (TIMEOUT, EOF)):
             pattern_list = [pattern_list]
 
         def prepare_pattern(pattern):
             if pattern in (TIMEOUT, EOF):
                 return pattern
             if isinstance(pattern, self.allowed_string_types):
                 return self._coerce_expect_string(pattern)
             self._pattern_type_err(pattern)
 
         try:
             pattern_list = iter(pattern_list)
         except TypeError:
             self._pattern_type_err(pattern_list)
         pattern_list = [prepare_pattern(p) for p in pattern_list]
         return self.expect_loop(searcher_string(pattern_list),
                 timeout, searchwindowsize)
 
     def expect_loop(self, searcher, timeout=-1, searchwindowsize=-1):
 
         '''This is the common loop used inside expect. The 'searcher' should be
         an instance of searcher_re or searcher_string, which describes how and
         what to search for in the input.
 
         See expect() for other arguments, return value and exceptions. '''
 
         self.searcher = searcher
 
         if timeout == -1:
             timeout = self.timeout
         if timeout is not None:
             end_time = time.time() + timeout
         if searchwindowsize == -1:
             searchwindowsize = self.searchwindowsize
 
         try:
             incoming = self.buffer
             freshlen = len(incoming)
             while True:
                 # Keep reading until exception or return.
                 index = searcher.search(incoming, freshlen, searchwindowsize)
                 if index >= 0:
                     self.buffer = incoming[searcher.end:]
                     self.before = incoming[: searcher.start]
                     self.after = incoming[searcher.start: searcher.end]
                     self.match = searcher.match
                     self.match_index = index
                     return self.match_index
                 # No match at this point
                 if (timeout is not None) and (timeout < 0):
                     raise TIMEOUT('Timeout exceeded in expect_any().')
                 # Still have time left, so read more data
                 c = self.read_nonblocking(self.maxread, timeout)
                 freshlen = len(c)
                 time.sleep(0.0001)
                 incoming = incoming + c
                 if timeout is not None:
                     timeout = end_time - time.time()
         except EOF:
             err = sys.exc_info()[1]
             self.buffer = self.string_type()
             self.before = incoming
             self.after = EOF
             index = searcher.eof_index
             if index >= 0:
                 self.match = EOF
                 self.match_index = index
                 return self.match_index
             else:
                 self.match = None
                 self.match_index = None
                 raise EOF(str(err) + '\n' + str(self))
         except TIMEOUT:
             err = sys.exc_info()[1]
             self.buffer = incoming
             self.before = incoming
             self.after = TIMEOUT
             index = searcher.timeout_index
             if index >= 0:
                 self.match = TIMEOUT
                 self.match_index = index
                 return self.match_index
             else:
                 self.match = None
                 self.match_index = None
                 raise TIMEOUT(str(err) + '\n' + str(self))
         except:
             self.before = incoming
             self.after = None
             self.match = None
             self.match_index = None
             raise
 
     def getwinsize(self):
 
         '''This returns the terminal window size of the child tty. The return
         value is a tuple of (rows, cols). '''
 
         TIOCGWINSZ = getattr(termios, 'TIOCGWINSZ', 1074295912)
         s = struct.pack('HHHH', 0, 0, 0, 0)
         x = fcntl.ioctl(self.child_fd, TIOCGWINSZ, s)
         return struct.unpack('HHHH', x)[0:2]
 
     def setwinsize(self, rows, cols):
 
         '''This sets the terminal window size of the child tty. This will cause
         a SIGWINCH signal to be sent to the child. This does not change the
         physical window size. It changes the size reported to TTY-aware
         applications like vi or curses -- applications that respond to the
         SIGWINCH signal. '''
 
         # Some very old platforms have a bug that causes the value for
         # termios.TIOCSWINSZ to be truncated. There was a hack here to work
         # around this, but it caused problems with newer platforms so has been
         # removed. For details see https://github.com/pexpect/pexpect/issues/39
         TIOCSWINSZ = getattr(termios, 'TIOCSWINSZ', -2146929561)
         # Note, assume ws_xpixel and ws_ypixel are zero.
         s = struct.pack('HHHH', rows, cols, 0, 0)
         fcntl.ioctl(self.fileno(), TIOCSWINSZ, s)
 
     def interact(self, escape_character=chr(29),
             input_filter=None, output_filter=None):
 
         '''This gives control of the child process to the interactive user (the
         human at the keyboard). Keystrokes are sent to the child process, and
         the stdout and stderr output of the child process is printed. This
         simply echos the child stdout and child stderr to the real stdout and
         it echos the real stdin to the child stdin. When the user types the
         escape_character this method will stop. The default for
         escape_character is ^]. This should not be confused with ASCII 27 --
         the ESC character. ASCII 29 was chosen for historical merit because
         this is the character used by 'telnet' as the escape character. The
         escape_character will not be sent to the child process.
 
         You may pass in optional input and output filter functions. These
         functions should take a string and return a string. The output_filter
         will be passed all the output from the child process. The input_filter
         will be passed all the keyboard input from the user. The input_filter
         is run BEFORE the check for the escape_character.
 
         Note that if you change the window size of the parent the SIGWINCH
         signal will not be passed through to the child. If you want the child
         window size to change when the parent's window size changes then do
         something like the following example::
 
             import pexpect, struct, fcntl, termios, signal, sys
             def sigwinch_passthrough (sig, data):
                 s = struct.pack("HHHH", 0, 0, 0, 0)
                 a = struct.unpack('hhhh', fcntl.ioctl(sys.stdout.fileno(),
                     termios.TIOCGWINSZ , s))
                 global p
                 p.setwinsize(a[0],a[1])
             # Note this 'p' global and used in sigwinch_passthrough.
             p = pexpect.spawn('/bin/bash')
             signal.signal(signal.SIGWINCH, sigwinch_passthrough)
             p.interact()
         '''
 
         # Flush the buffer.
         self.write_to_stdout(self.buffer)
         self.stdout.flush()
         self.buffer = self.string_type()
         mode = tty.tcgetattr(self.STDIN_FILENO)
         tty.setraw(self.STDIN_FILENO)
         if PY3:
             escape_character = escape_character.encode('latin-1')
         try:
             self.__interact_copy(escape_character, input_filter, output_filter)
         finally:
             tty.tcsetattr(self.STDIN_FILENO, tty.TCSAFLUSH, mode)
 
     def __interact_writen(self, fd, data):
         '''This is used by the interact() method.
         '''
 
         while data != b'' and self.isalive():
             n = os.write(fd, data)
             data = data[n:]
 
     def __interact_read(self, fd):
         '''This is used by the interact() method.
         '''
 
         return os.read(fd, 1000)
 
     def __interact_copy(self, escape_character=None,
             input_filter=None, output_filter=None):
 
         '''This is used by the interact() method.
         '''
 
         while self.isalive():
             r, w, e = self.__select([self.child_fd, self.STDIN_FILENO], [], [])
             if self.child_fd in r:
                 try:
                     data = self.__interact_read(self.child_fd)
-                except OSError as e:
-                    # The subprocess may have closed before we get to reading it
-                    if e.errno != errno.EIO:
+                except OSError as err:
+                    if err.args[0] == errno.EIO:
+                        # Linux-style EOF
+                        break
                         raise
+                if data == b'':
+                    # BSD-style EOF
+                    break
                 if output_filter:
                     data = output_filter(data)
                 if self.logfile is not None:
                     self.logfile.write(data)
                     self.logfile.flush()
                 os.write(self.STDOUT_FILENO, data)
             if self.STDIN_FILENO in r:
                 data = self.__interact_read(self.STDIN_FILENO)
                 if input_filter:
                     data = input_filter(data)
                 i = data.rfind(escape_character)
                 if i != -1:
                     data = data[:i]
                     self.__interact_writen(self.child_fd, data)
                     break
                 self.__interact_writen(self.child_fd, data)
 
     def __select(self, iwtd, owtd, ewtd, timeout=None):
 
         '''This is a wrapper around select.select() that ignores signals. If
         select.select raises a select.error exception and errno is an EINTR
         error then it is ignored. Mainly this is used to ignore sigwinch
         (terminal resize). '''
 
         # if select() is interrupted by a signal (errno==EINTR) then
         # we loop back and enter the select() again.
         if timeout is not None:
             end_time = time.time() + timeout
         while True:
             try:
                 return select.select(iwtd, owtd, ewtd, timeout)
             except select.error:
                 err = sys.exc_info()[1]
                 if err.args[0] == errno.EINTR:
                     # if we loop back we have to subtract the
                     # amount of time we already waited.
                     if timeout is not None:
                         timeout = end_time - time.time()
                         if timeout < 0:
                             return([], [], [])
                 else:
                     # something else caused the select.error, so
                     # this actually is an exception.
                     raise
 
 ##############################################################################
 # The following methods are no longer supported or allowed.
 
-    def setmaxread(self, maxread):
+    def setmaxread(self, maxread): # pragma: no cover
 
         '''This method is no longer supported or allowed. I don't like getters
         and setters without a good reason. '''
 
         raise ExceptionPexpect('This method is no longer supported ' +
                 'or allowed. Just assign a value to the ' +
                 'maxread member variable.')
 
-    def setlog(self, fileobject):
+    def setlog(self, fileobject): # pragma: no cover
 
         '''This method is no longer supported or allowed.
         '''
 
         raise ExceptionPexpect('This method is no longer supported ' +
                 'or allowed. Just assign a value to the logfile ' +
                 'member variable.')
 
 ##############################################################################
 # End of spawn class
 ##############################################################################
 
 class spawnu(spawn):
     """Works like spawn, but accepts and returns unicode strings.
 
     Extra parameters:
 
     :param encoding: The encoding to use for communications (default: 'utf-8')
     :param errors: How to handle encoding/decoding errors; one of 'strict'
                    (the default), 'ignore', or 'replace', as described
                    for :meth:`~bytes.decode` and :meth:`~str.encode`.
     """
     if PY3:
         string_type = str
         allowed_string_types = (str, )
         _chr = staticmethod(chr)
         linesep = os.linesep
+        crlf = '\r\n'
     else:
         string_type = unicode
         allowed_string_types = (unicode, )
         _chr = staticmethod(unichr)
         linesep = os.linesep.decode('ascii')
+        crlf = '\r\n'.decode('ascii')
     # This can handle unicode in both Python 2 and 3
     write_to_stdout = sys.stdout.write
 
     def __init__(self, *args, **kwargs):
         self.encoding = kwargs.pop('encoding', 'utf-8')
         self.errors = kwargs.pop('errors', 'strict')
         self._decoder = codecs.getincrementaldecoder(self.encoding)(errors=self.errors)
         super(spawnu, self).__init__(*args, **kwargs)
 
     @staticmethod
     def _coerce_expect_string(s):
         return s
 
     @staticmethod
     def _coerce_send_string(s):
         return s
 
     def _coerce_read_string(self, s):
         return self._decoder.decode(s, final=False)
 
     def _send(self, s):
         return os.write(self.child_fd, s.encode(self.encoding, self.errors))
 
 
 class searcher_string(object):
 
     '''This is a plain string search helper for the spawn.expect_any() method.
     This helper class is for speed. For more powerful regex patterns
     see the helper class, searcher_re.
 
     Attributes:
 
         eof_index     - index of EOF, or -1
         timeout_index - index of TIMEOUT, or -1
 
     After a successful match by the search() method the following attributes
     are available:
 
         start - index into the buffer, first byte of match
         end   - index into the buffer, first byte after match
         match - the matching string itself
 
     '''
 
     def __init__(self, strings):
 
         '''This creates an instance of searcher_string. This argument 'strings'
         may be a list; a sequence of strings; or the EOF or TIMEOUT types. '''
 
         self.eof_index = -1
         self.timeout_index = -1
         self._strings = []
         for n, s in enumerate(strings):
             if s is EOF:
                 self.eof_index = n
                 continue
             if s is TIMEOUT:
                 self.timeout_index = n
                 continue
             self._strings.append((n, s))
 
     def __str__(self):
 
         '''This returns a human-readable string that represents the state of
         the object.'''
 
         ss = [(ns[0], '    %d: "%s"' % ns) for ns in self._strings]
         ss.append((-1, 'searcher_string:'))
         if self.eof_index >= 0:
             ss.append((self.eof_index, '    %d: EOF' % self.eof_index))
         if self.timeout_index >= 0:
             ss.append((self.timeout_index,
                 '    %d: TIMEOUT' % self.timeout_index))
         ss.sort()
         ss = list(zip(*ss))[1]
         return '\n'.join(ss)
 
     def search(self, buffer, freshlen, searchwindowsize=None):
 
         '''This searches 'buffer' for the first occurence of one of the search
         strings.  'freshlen' must indicate the number of bytes at the end of
         'buffer' which have not been searched before. It helps to avoid
         searching the same, possibly big, buffer over and over again.
 
         See class spawn for the 'searchwindowsize' argument.
 
         If there is a match this returns the index of that string, and sets
         'start', 'end' and 'match'. Otherwise, this returns -1. '''
 
         first_match = None
 
         # 'freshlen' helps a lot here. Further optimizations could
         # possibly include:
         #
         # using something like the Boyer-Moore Fast String Searching
         # Algorithm; pre-compiling the search through a list of
         # strings into something that can scan the input once to
         # search for all N strings; realize that if we search for
         # ['bar', 'baz'] and the input is '...foo' we need not bother
         # rescanning until we've read three more bytes.
         #
         # Sadly, I don't know enough about this interesting topic. /grahn
 
         for index, s in self._strings:
             if searchwindowsize is None:
                 # the match, if any, can only be in the fresh data,
                 # or at the very end of the old data
                 offset = -(freshlen + len(s))
             else:
                 # better obey searchwindowsize
                 offset = -searchwindowsize
             n = buffer.find(s, offset)
             if n >= 0 and (first_match is None or n < first_match):
                 first_match = n
                 best_index, best_match = index, s
         if first_match is None:
             return -1
         self.match = best_match
         self.start = first_match
         self.end = self.start + len(self.match)
         return best_index
 
 
 class searcher_re(object):
 
     '''This is regular expression string search helper for the
     spawn.expect_any() method. This helper class is for powerful
     pattern matching. For speed, see the helper class, searcher_string.
 
     Attributes:
 
         eof_index     - index of EOF, or -1
         timeout_index - index of TIMEOUT, or -1
 
     After a successful match by the search() method the following attributes
     are available:
 
         start - index into the buffer, first byte of match
         end   - index into the buffer, first byte after match
         match - the re.match object returned by a succesful re.search
 
     '''
 
     def __init__(self, patterns):
 
         '''This creates an instance that searches for 'patterns' Where
         'patterns' may be a list or other sequence of compiled regular
         expressions, or the EOF or TIMEOUT types.'''
 
         self.eof_index = -1
         self.timeout_index = -1
         self._searches = []
         for n, s in zip(list(range(len(patterns))), patterns):
             if s is EOF:
                 self.eof_index = n
                 continue
             if s is TIMEOUT:
                 self.timeout_index = n
                 continue
             self._searches.append((n, s))
 
     def __str__(self):
 
         '''This returns a human-readable string that represents the state of
         the object.'''
 
         #ss = [(n, '    %d: re.compile("%s")' %
         #    (n, repr(s.pattern))) for n, s in self._searches]
         ss = list()
         for n, s in self._searches:
             try:
                 ss.append((n, '    %d: re.compile("%s")' % (n, s.pattern)))
             except UnicodeEncodeError:
                 # for test cases that display __str__ of searches, dont throw
                 # another exception just because stdout is ascii-only, using
                 # repr()
                 ss.append((n, '    %d: re.compile(%r)' % (n, s.pattern)))
         ss.append((-1, 'searcher_re:'))
         if self.eof_index >= 0:
             ss.append((self.eof_index, '    %d: EOF' % self.eof_index))
         if self.timeout_index >= 0:
             ss.append((self.timeout_index, '    %d: TIMEOUT' %
                 self.timeout_index))
         ss.sort()
         ss = list(zip(*ss))[1]
         return '\n'.join(ss)
 
     def search(self, buffer, freshlen, searchwindowsize=None):
 
         '''This searches 'buffer' for the first occurence of one of the regular
         expressions. 'freshlen' must indicate the number of bytes at the end of
         'buffer' which have not been searched before.
 
         See class spawn for the 'searchwindowsize' argument.
 
         If there is a match this returns the index of that string, and sets
         'start', 'end' and 'match'. Otherwise, returns -1.'''
 
         first_match = None
         # 'freshlen' doesn't help here -- we cannot predict the
         # length of a match, and the re module provides no help.
         if searchwindowsize is None:
             searchstart = 0
         else:
             searchstart = max(0, len(buffer) - searchwindowsize)
         for index, s in self._searches:
             match = s.search(buffer, searchstart)
             if match is None:
                 continue
             n = match.start()
             if first_match is None or n < first_match:
                 first_match = n
                 the_match = match
                 best_index = index
         if first_match is None:
             return -1
         self.start = first_match
         self.match = the_match
         self.end = self.match.end()
         return best_index
 
 
-def which(filename):
+def is_executable_file(path):
+    """Checks that path is an executable regular file (or a symlink to a file).
+    
+    This is roughly ``os.path isfile(path) and os.access(path, os.X_OK)``, but
+    on some platforms :func:`os.access` gives us the wrong answer, so this
+    checks permission bits directly.
+    """
+    # follow symlinks,
+    fpath = os.path.realpath(path)
+
+    # return False for non-files (directories, fifo, etc.)
+    if not os.path.isfile(fpath):
+        return False
+
+    # On Solaris, etc., "If the process has appropriate privileges, an
+    # implementation may indicate success for X_OK even if none of the
+    # execute file permission bits are set."
+    #
+    # For this reason, it is necessary to explicitly check st_mode
 
+    # get file mode using os.stat, and check if `other',
+    # that is anybody, may read and execute.
+    mode = os.stat(fpath).st_mode
+    if mode & stat.S_IROTH and mode & stat.S_IXOTH:
+        return True
+
+    # get current user's group ids, and check if `group',
+    # when matching ours, may read and execute.
+    user_gids = os.getgroups() + [os.getgid()]
+    if (os.stat(fpath).st_gid in user_gids and
+            mode & stat.S_IRGRP and mode & stat.S_IXGRP):
+        return True
+
+    # finally, if file owner matches our effective userid,
+    # check if `user', may read and execute.
+    user_gids = os.getgroups() + [os.getgid()]
+    if (os.stat(fpath).st_uid == os.geteuid() and
+            mode & stat.S_IRUSR and mode & stat.S_IXUSR):
+        return True
+
+    return False
+
+def which(filename):
     '''This takes a given filename; tries to find it in the environment path;
     then checks if it is executable. This returns the full path to the filename
     if found and executable. Otherwise this returns None.'''
 
     # Special case where filename contains an explicit path.
-    if os.path.dirname(filename) != '':
-        if os.access(filename, os.X_OK):
+    if os.path.dirname(filename) != '' and is_executable_file(filename):
             return filename
     if 'PATH' not in os.environ or os.environ['PATH'] == '':
         p = os.defpath
     else:
         p = os.environ['PATH']
     pathlist = p.split(os.pathsep)
     for path in pathlist:
         ff = os.path.join(path, filename)
-        if os.access(ff, os.X_OK):
+        if is_executable_file(ff):
             return ff
     return None
 
 
 def split_command_line(command_line):
 
     '''This splits a command line into a list of arguments. It splits arguments
     on spaces, but handles embedded quotes, doublequotes, and escaped
     characters. It's impossible to do this with a regular expression, so I
     wrote a little state machine to parse the command line. '''
 
     arg_list = []
     arg = ''
 
     # Constants to name the states we can be in.
     state_basic = 0
     state_esc = 1
     state_singlequote = 2
     state_doublequote = 3
     # The state when consuming whitespace between commands.
     state_whitespace = 4
     state = state_basic
 
     for c in command_line:
         if state == state_basic or state == state_whitespace:
             if c == '\\':
                 # Escape the next character
                 state = state_esc
             elif c == r"'":
                 # Handle single quote
                 state = state_singlequote
             elif c == r'"':
                 # Handle double quote
                 state = state_doublequote
             elif c.isspace():
                 # Add arg to arg_list if we aren't in the middle of whitespace.
                 if state == state_whitespace:
                     # Do nothing.
                     None
                 else:
                     arg_list.append(arg)
                     arg = ''
                     state = state_whitespace
             else:
                 arg = arg + c
                 state = state_basic
         elif state == state_esc:
             arg = arg + c
             state = state_basic
         elif state == state_singlequote:
             if c == r"'":
                 state = state_basic
             else:
                 arg = arg + c
         elif state == state_doublequote:
             if c == r'"':
                 state = state_basic
             else:
                 arg = arg + c
 
     if arg != '':
         arg_list.append(arg)
     return arg_list
 
-# vi:set sr et ts=4 sw=4 ft=python :
+# vim: set shiftround expandtab tabstop=4 shiftwidth=4 ft=python autoindent :