Use proper subprocess commands instead of modifying the command line.

This should in particular work on windows; as 2>/dev/null might not have
been proper windows syntax

IPython/core/page.py

@@ -1,366 +1,372 b''
 # encoding: utf-8
 """
 Paging capabilities for IPython.core
 
 Notes
 -----
 
 For now this uses IPython hooks, so it can't be in IPython.utils.  If we can get
 rid of that dependency, we could move it there.
 -----
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 
 import os
+import io
 import re
 import sys
 import tempfile
+import subprocess
 
 from io import UnsupportedOperation
 
 from IPython import get_ipython
 from IPython.core.display import display
 from IPython.core.error import TryNext
 from IPython.utils.data import chop
 from IPython.utils.process import system
 from IPython.utils.terminal import get_terminal_size
 from IPython.utils import py3compat
 
 
 def display_page(strng, start=0, screen_lines=25):
     """Just display, no paging. screen_lines is ignored."""
     if isinstance(strng, dict):
         data = strng
     else:
         if start:
             strng = u'\n'.join(strng.splitlines()[start:])
         data = { 'text/plain': strng }
     display(data, raw=True)
 
 
 def as_hook(page_func):
     """Wrap a pager func to strip the `self` arg
     
     so it can be called as a hook.
     """
     return lambda self, *args, **kwargs: page_func(*args, **kwargs)
 
 
 esc_re = re.compile(r"(\x1b[^m]+m)")
 
 def page_dumb(strng, start=0, screen_lines=25):
     """Very dumb 'pager' in Python, for when nothing else works.
 
     Only moves forward, same interface as page(), except for pager_cmd and
     mode.
     """
     if isinstance(strng, dict):
         strng = strng.get('text/plain', '')
     out_ln  = strng.splitlines()[start:]
     screens = chop(out_ln,screen_lines-1)
     if len(screens) == 1:
         print(os.linesep.join(screens[0]))
     else:
         last_escape = ""
         for scr in screens[0:-1]:
             hunk = os.linesep.join(scr)
             print(last_escape + hunk)
             if not page_more():
                 return
             esc_list = esc_re.findall(hunk)
             if len(esc_list) > 0:
                 last_escape = esc_list[-1]
         print(last_escape + os.linesep.join(screens[-1]))
 
 def _detect_screen_size(screen_lines_def):
     """Attempt to work out the number of lines on the screen.
 
     This is called by page(). It can raise an error (e.g. when run in the
     test suite), so it's separated out so it can easily be called in a try block.
     """
     TERM = os.environ.get('TERM',None)
     if not((TERM=='xterm' or TERM=='xterm-color') and sys.platform != 'sunos5'):
         # curses causes problems on many terminals other than xterm, and
         # some termios calls lock up on Sun OS5.
         return screen_lines_def
     
     try:
         import termios
         import curses
     except ImportError:
         return screen_lines_def
     
     # There is a bug in curses, where *sometimes* it fails to properly
     # initialize, and then after the endwin() call is made, the
     # terminal is left in an unusable state.  Rather than trying to
     # check every time for this (by requesting and comparing termios
     # flags each time), we just save the initial terminal state and
     # unconditionally reset it every time.  It's cheaper than making
     # the checks.
     try:
         term_flags = termios.tcgetattr(sys.stdout)
     except termios.error as err:
         # can fail on Linux 2.6, pager_page will catch the TypeError
         raise TypeError('termios error: {0}'.format(err))
 
     try:
         scr = curses.initscr()
     except AttributeError:
         # Curses on Solaris may not be complete, so we can't use it there
         return screen_lines_def
     
     screen_lines_real,screen_cols = scr.getmaxyx()
     curses.endwin()
 
     # Restore terminal state in case endwin() didn't.
     termios.tcsetattr(sys.stdout,termios.TCSANOW,term_flags)
     # Now we have what we needed: the screen size in rows/columns
     return screen_lines_real
     #print '***Screen size:',screen_lines_real,'lines x',\
     #screen_cols,'columns.' # dbg
 
 def pager_page(strng, start=0, screen_lines=0, pager_cmd=None):
     """Display a string, piping through a pager after a certain length.
     
     strng can be a mime-bundle dict, supplying multiple representations,
     keyed by mime-type.
 
     The screen_lines parameter specifies the number of *usable* lines of your
     terminal screen (total lines minus lines you need to reserve to show other
     information).
 
     If you set screen_lines to a number <=0, page() will try to auto-determine
     your screen size and will only use up to (screen_size+screen_lines) for
     printing, paging after that. That is, if you want auto-detection but need
     to reserve the bottom 3 lines of the screen, use screen_lines = -3, and for
     auto-detection without any lines reserved simply use screen_lines = 0.
 
     If a string won't fit in the allowed lines, it is sent through the
     specified pager command. If none given, look for PAGER in the environment,
     and ultimately default to less.
 
     If no system pager works, the string is sent through a 'dumb pager'
     written in python, very simplistic.
     """
     
     # for compatibility with mime-bundle form:
     if isinstance(strng, dict):
         strng = strng['text/plain']
 
     # Ugly kludge, but calling curses.initscr() flat out crashes in emacs
     TERM = os.environ.get('TERM','dumb')
     if TERM in ['dumb','emacs'] and os.name != 'nt':
         print(strng)
         return
     # chop off the topmost part of the string we don't want to see
     str_lines = strng.splitlines()[start:]
     str_toprint = os.linesep.join(str_lines)
     num_newlines = len(str_lines)
     len_str = len(str_toprint)
 
     # Dumb heuristics to guesstimate number of on-screen lines the string
     # takes.  Very basic, but good enough for docstrings in reasonable
     # terminals. If someone later feels like refining it, it's not hard.
     numlines = max(num_newlines,int(len_str/80)+1)
 
     screen_lines_def = get_terminal_size()[1]
 
     # auto-determine screen size
     if screen_lines <= 0:
         try:
             screen_lines += _detect_screen_size(screen_lines_def)
         except (TypeError, UnsupportedOperation):
             print(str_toprint)
             return
 
     #print 'numlines',numlines,'screenlines',screen_lines  # dbg
     if numlines <= screen_lines :
         #print '*** normal print'  # dbg
         print(str_toprint)
     else:
         # Try to open pager and default to internal one if that fails.
         # All failure modes are tagged as 'retval=1', to match the return
         # value of a failed system command.  If any intermediate attempt
         # sets retval to 1, at the end we resort to our own page_dumb() pager.
         pager_cmd = get_pager_cmd(pager_cmd)
         pager_cmd += ' ' + get_pager_start(pager_cmd,start)
         if os.name == 'nt':
             if pager_cmd.startswith('type'):
                 # The default WinXP 'type' command is failing on complex strings.
                 retval = 1
             else:
                 fd, tmpname = tempfile.mkstemp('.txt')
                 try:
                     os.close(fd)
                     with open(tmpname, 'wt') as tmpfile:
                         tmpfile.write(strng)
                         cmd = "%s < %s" % (pager_cmd, tmpname)
                     # tmpfile needs to be closed for windows
                     if os.system(cmd):
                         retval = 1
                     else:
                         retval = None
                 finally:
                     os.remove(tmpname)
         else:
             try:
                 retval = None
-                # if I use popen4, things hang. No idea why.
-                #pager,shell_out = os.popen4(pager_cmd)
-                pager = os.popen(pager_cmd + ' 2>/dev/null', 'w')
+                # Emulate os.popen, but redirect stderr
+                proc = subprocess.Popen(pager_cmd,
+                                shell=True,
+                                stdin=subprocess.PIPE,
+                                stderr=subprocess.DEVNULL
+                                )
+                pager = os._wrap_close(io.TextIOWrapper(proc.stdin), proc)
                 try:
                     pager_encoding = pager.encoding or sys.stdout.encoding
                     pager.write(strng)
                 finally:
                     retval = pager.close()
             except IOError as msg:  # broken pipe when user quits
                 if msg.args == (32, 'Broken pipe'):
                     retval = None
                 else:
                     retval = 1
             except OSError:
                 # Other strange problems, sometimes seen in Win2k/cygwin
                 retval = 1
         if retval is not None:
             page_dumb(strng,screen_lines=screen_lines)
 
 
 def page(data, start=0, screen_lines=0, pager_cmd=None):
     """Display content in a pager, piping through a pager after a certain length.
     
     data can be a mime-bundle dict, supplying multiple representations,
     keyed by mime-type, or text.
     
     Pager is dispatched via the `show_in_pager` IPython hook.
     If no hook is registered, `pager_page` will be used.
     """
     # Some routines may auto-compute start offsets incorrectly and pass a
     # negative value.  Offset to 0 for robustness.
     start = max(0, start)
 
     # first, try the hook
     ip = get_ipython()
     if ip:
         try:
             ip.hooks.show_in_pager(data, start=start, screen_lines=screen_lines)
             return
         except TryNext:
             pass
     
     # fallback on default pager
     return pager_page(data, start, screen_lines, pager_cmd)
 
 
 def page_file(fname, start=0, pager_cmd=None):
     """Page a file, using an optional pager command and starting line.
     """
 
     pager_cmd = get_pager_cmd(pager_cmd)
     pager_cmd += ' ' + get_pager_start(pager_cmd,start)
 
     try:
         if os.environ['TERM'] in ['emacs','dumb']:
             raise EnvironmentError
         system(pager_cmd + ' ' + fname)
     except:
         try:
             if start > 0:
                 start -= 1
             page(open(fname).read(),start)
         except:
             print('Unable to show file',repr(fname))
 
 
 def get_pager_cmd(pager_cmd=None):
     """Return a pager command.
 
     Makes some attempts at finding an OS-correct one.
     """
     if os.name == 'posix':
         default_pager_cmd = 'less -R'  # -R for color control sequences
     elif os.name in ['nt','dos']:
         default_pager_cmd = 'type'
 
     if pager_cmd is None:
         try:
             pager_cmd = os.environ['PAGER']
         except:
             pager_cmd = default_pager_cmd
     
     if pager_cmd == 'less' and '-r' not in os.environ.get('LESS', '').lower():
         pager_cmd += ' -R'
     
     return pager_cmd
 
 
 def get_pager_start(pager, start):
     """Return the string for paging files with an offset.
 
     This is the '+N' argument which less and more (under Unix) accept.
     """
 
     if pager in ['less','more']:
         if start:
             start_string = '+' + str(start)
         else:
             start_string = ''
     else:
         start_string = ''
     return start_string
 
 
 # (X)emacs on win32 doesn't like to be bypassed with msvcrt.getch()
 if os.name == 'nt' and os.environ.get('TERM','dumb') != 'emacs':
     import msvcrt
     def page_more():
         """ Smart pausing between pages
 
         @return:    True if need print more lines, False if quit
         """
         sys.stdout.write('---Return to continue, q to quit--- ')
         ans = msvcrt.getwch()
         if ans in ("q", "Q"):
             result = False
         else:
             result = True
         sys.stdout.write("\b"*37 + " "*37 + "\b"*37)
         return result
 else:
     def page_more():
         ans = py3compat.input('---Return to continue, q to quit--- ')
         if ans.lower().startswith('q'):
             return False
         else:
             return True
 
 
 def snip_print(str,width = 75,print_full = 0,header = ''):
     """Print a string snipping the midsection to fit in width.
 
     print_full: mode control:
     
       - 0: only snip long strings
       - 1: send to page() directly.
       - 2: snip long strings and ask for full length viewing with page()
     
     Return 1 if snipping was necessary, 0 otherwise."""
 
     if print_full == 1:
         page(header+str)
         return 0
 
     print(header, end=' ')
     if len(str) < width:
         print(str)
         snip = 0
     else:
         whalf = int((width -5)/2)
         print(str[:whalf] + ' <...> ' + str[-whalf:])
         snip = 1
     if snip and print_full == 2:
         if py3compat.input(header+' Snipped. View (y/n)? [N]').lower() == 'y':
             page(str)
     return snip