Fix bug where 'if 1:' was being added to comment-only code.

Found by trying to paste and run this example:
http://matplotlib.sourceforge.net/examples/api/collections_demo.html

that happened to have indented, comment-only lines of the type:

code()
   # comment
code()

In these cases, we should *not* try to prepend 'if 1:' to the user's
code since that comment by itself isn't executable, and it will cause
a compiler IndentationError.

IPython/core/inputsplitter.py

@@ -1,954 +1,960 b''
 """Analysis of text input into executable blocks.
 
 The main class in this module, :class:`InputSplitter`, is designed to break
 input from either interactive, line-by-line environments or block-based ones,
 into standalone blocks that can be executed by Python as 'single' statements
 (thus triggering sys.displayhook).
 
 A companion, :class:`IPythonInputSplitter`, provides the same functionality but
 with full support for the extended IPython syntax (magics, system calls, etc).
 
 For more details, see the class docstring below.
 
 Syntax Transformations
 ----------------------
 
 One of the main jobs of the code in this file is to apply all syntax
 transformations that make up 'the IPython language', i.e. magics, shell
 escapes, etc.  All transformations should be implemented as *fully stateless*
 entities, that simply take one line as their input and return a line.
 Internally for implementation purposes they may be a normal function or a
 callable object, but the only input they receive will be a single line and they
 should only return a line, without holding any data-dependent state between
 calls.
 
 As an example, the EscapedTransformer is a class so we can more clearly group
 together the functionality of dispatching to individual functions based on the
 starting escape character, but the only method for public use is its call
 method.
 
 
 ToDo
 ----
 
 - Should we make push() actually raise an exception once push_accepts_more()
   returns False?
 
 - Naming cleanups.  The tr_* names aren't the most elegant, though now they are
   at least just attributes of a class so not really very exposed.
 
 - Think about the best way to support dynamic things: automagic, autocall,
   macros, etc.
 
 - Think of a better heuristic for the application of the transforms in
   IPythonInputSplitter.push() than looking at the buffer ending in ':'.  Idea:
   track indentation change events (indent, dedent, nothing) and apply them only
   if the indentation went up, but not otherwise.
 
 - Think of the cleanest way for supporting user-specified transformations (the
   user prefilters we had before).
 
 Authors
 -------
 
 * Fernando Perez
 * Brian Granger
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2010  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 # stdlib
 import codeop
 import re
 import sys
 
 # IPython modules
 from IPython.utils.text import make_quoted_expr
 #-----------------------------------------------------------------------------
 # Globals
 #-----------------------------------------------------------------------------
 
 # The escape sequences that define the syntax transformations IPython will
 # apply to user input.  These can NOT be just changed here: many regular
 # expressions and other parts of the code may use their hardcoded values, and
 # for all intents and purposes they constitute the 'IPython syntax', so they
 # should be considered fixed.
 
 ESC_SHELL  = '!'
 ESC_SH_CAP = '!!'
 ESC_HELP   = '?'
 ESC_HELP2  = '??'
 ESC_MAGIC  = '%'
 ESC_QUOTE  = ','
 ESC_QUOTE2 = ';'
 ESC_PAREN  = '/'
 
 #-----------------------------------------------------------------------------
 # Utilities
 #-----------------------------------------------------------------------------
 
 # FIXME: These are general-purpose utilities that later can be moved to the
 # general ward.  Kept here for now because we're being very strict about test
 # coverage with this code, and this lets us ensure that we keep 100% coverage
 # while developing.
 
 # compiled regexps for autoindent management
 dedent_re = re.compile(r'^\s+raise|^\s+return|^\s+pass')
 ini_spaces_re = re.compile(r'^([ \t\r\f\v]+)')
 
+# regexp to match pure comment lines so we don't accidentally insert 'if 1:'
+# before pure comments
+comment_line_re = re.compile('^\s*\#')
+
 
 def num_ini_spaces(s):
     """Return the number of initial spaces in a string.
 
     Note that tabs are counted as a single space.  For now, we do *not* support
     mixing of tabs and spaces in the user's input.
 
     Parameters
     ----------
     s : string
 
     Returns
     -------
     n : int
     """
 
     ini_spaces = ini_spaces_re.match(s)
     if ini_spaces:
         return ini_spaces.end()
     else:
         return 0
 
 
 def remove_comments(src):
     """Remove all comments from input source.
 
     Note: comments are NOT recognized inside of strings!
 
     Parameters
     ----------
     src : string
       A single or multiline input string.
 
     Returns
     -------
     String with all Python comments removed.
     """
 
     return re.sub('#.*', '', src)
 
 
 def get_input_encoding():
     """Return the default standard input encoding.
 
     If sys.stdin has no encoding, 'ascii' is returned."""
     # There are strange environments for which sys.stdin.encoding is None. We
     # ensure that a valid encoding is returned.
     encoding = getattr(sys.stdin, 'encoding', None)
     if encoding is None:
         encoding = 'ascii'
     return encoding
 
 #-----------------------------------------------------------------------------
 # Classes and functions for normal Python syntax handling
 #-----------------------------------------------------------------------------
 
 # HACK!  This implementation, written by Robert K a while ago using the
 # compiler module, is more robust than the other one below, but it expects its
 # input to be pure python (no ipython syntax).  For now we're using it as a
 # second-pass splitter after the first pass transforms the input to pure
 # python.
 
 def split_blocks(python):
     """ Split multiple lines of code into discrete commands that can be
     executed singly.
 
     Parameters
     ----------
     python : str
         Pure, exec'able Python code.
 
     Returns
     -------
     commands : list of str
         Separate commands that can be exec'ed independently.
     """
 
     import compiler
     
     # compiler.parse treats trailing spaces after a newline as a
     # SyntaxError.  This is different than codeop.CommandCompiler, which
     # will compile the trailng spaces just fine.  We simply strip any
     # trailing whitespace off.  Passing a string with trailing whitespace
     # to exec will fail however.  There seems to be some inconsistency in
     # how trailing whitespace is handled, but this seems to work.
     python_ori = python # save original in case we bail on error
     python = python.strip()
 
     # The compiler module does not like unicode. We need to convert
     # it encode it:
     if isinstance(python, unicode):
         # Use the utf-8-sig BOM so the compiler detects this a UTF-8
         # encode string.
         python = '\xef\xbb\xbf' + python.encode('utf-8')
 
     # The compiler module will parse the code into an abstract syntax tree.
     # This has a bug with str("a\nb"), but not str("""a\nb""")!!!
     try:
         ast = compiler.parse(python)
     except:
         return [python_ori]
 
     # Uncomment to help debug the ast tree
     # for n in ast.node:
     #     print n.lineno,'->',n
 
     # Each separate command is available by iterating over ast.node. The
     # lineno attribute is the line number (1-indexed) beginning the commands
     # suite.
     # lines ending with ";" yield a Discard Node that doesn't have a lineno
     # attribute.  These nodes can and should be discarded.  But there are
     # other situations that cause Discard nodes that shouldn't be discarded.
     # We might eventually discover other cases where lineno is None and have
     # to put in a more sophisticated test.
     linenos = [x.lineno-1 for x in ast.node if x.lineno is not None]
 
     # When we finally get the slices, we will need to slice all the way to
     # the end even though we don't have a line number for it. Fortunately,
     # None does the job nicely.
     linenos.append(None)
 
     # Same problem at the other end: sometimes the ast tree has its
     # first complete statement not starting on line 0. In this case
     # we might miss part of it.  This fixes ticket 266993.  Thanks Gael!
     linenos[0] = 0
 
     lines = python.splitlines()
 
     # Create a list of atomic commands.
     cmds = []
     for i, j in zip(linenos[:-1], linenos[1:]):
         cmd = lines[i:j]
         if cmd:
             cmds.append('\n'.join(cmd)+'\n')
 
     return cmds
 
 
 class InputSplitter(object):
     """An object that can split Python source input in executable blocks.
 
     This object is designed to be used in one of two basic modes:
 
     1. By feeding it python source line-by-line, using :meth:`push`.  In this
        mode, it will return on each push whether the currently pushed code
        could be executed already.  In addition, it provides a method called
        :meth:`push_accepts_more` that can be used to query whether more input
        can be pushed into a single interactive block.
 
     2. By calling :meth:`split_blocks` with a single, multiline Python string,
        that is then split into blocks each of which can be executed
        interactively as a single statement.
 
     This is a simple example of how an interactive terminal-based client can use
     this tool::
 
         isp = InputSplitter()
         while isp.push_accepts_more():
             indent = ' '*isp.indent_spaces
             prompt = '>>> ' + indent
             line = indent + raw_input(prompt)
             isp.push(line)
         print 'Input source was:\n', isp.source_reset(),
     """
     # Number of spaces of indentation computed from input that has been pushed
     # so far.  This is the attributes callers should query to get the current
     # indentation level, in order to provide auto-indent facilities.
     indent_spaces = 0
     # String, indicating the default input encoding.  It is computed by default
     # at initialization time via get_input_encoding(), but it can be reset by a
     # client with specific knowledge of the encoding.
     encoding = ''
     # String where the current full source input is stored, properly encoded.
     # Reading this attribute is the normal way of querying the currently pushed
     # source code, that has been properly encoded.
     source = ''
     # Code object corresponding to the current source.  It is automatically
     # synced to the source, so it can be queried at any time to obtain the code
     # object; it will be None if the source doesn't compile to valid Python.
     code = None
     # Input mode
     input_mode = 'line'
     
     # Private attributes
     
     # List with lines of input accumulated so far
     _buffer = None
     # Command compiler
     _compile = None
     # Mark when input has changed indentation all the way back to flush-left
     _full_dedent = False
     # Boolean indicating whether the current block is complete
     _is_complete = None
     
     def __init__(self, input_mode=None):
         """Create a new InputSplitter instance.
 
         Parameters
         ----------
         input_mode : str
 
           One of ['line', 'block']; default is 'line'.
 
        The input_mode parameter controls how new inputs are used when fed via
        the :meth:`push` method:
 
        - 'line': meant for line-oriented clients, inputs are appended one at a
          time to the internal buffer and the whole buffer is compiled.
 
        - 'block': meant for clients that can edit multi-line blocks of text at
           a time.  Each new input new input completely replaces all prior
           inputs.  Block mode is thus equivalent to prepending a full reset()
           to every push() call.
         """
         self._buffer = []
         self._compile = codeop.CommandCompiler()
         self.encoding = get_input_encoding()
         self.input_mode = InputSplitter.input_mode if input_mode is None \
                           else input_mode
 
     def reset(self):
         """Reset the input buffer and associated state."""
         self.indent_spaces = 0
         self._buffer[:] = []
         self.source = ''
         self.code = None
         self._is_complete = False
         self._full_dedent = False
 
     def source_reset(self):
         """Return the input source and perform a full reset.
         """
         out = self.source
         self.reset()
         return out
 
     def push(self, lines):
         """Push one ore more lines of input.
 
         This stores the given lines and returns a status code indicating
         whether the code forms a complete Python block or not.
 
         Any exceptions generated in compilation are swallowed, but if an
         exception was produced, the method returns True.
 
         Parameters
         ----------
         lines : string
           One or more lines of Python input.
         
         Returns
         -------
         is_complete : boolean
           True if the current input source (the result of the current input
         plus prior inputs) forms a complete Python execution block.  Note that
         this value is also stored as a private attribute (_is_complete), so it
         can be queried at any time.
         """
         if self.input_mode == 'block':
             self.reset()
         
         # If the source code has leading blanks, add 'if 1:\n' to it
         # this allows execution of indented pasted code. It is tempting
         # to add '\n' at the end of source to run commands like ' a=1'
         # directly, but this fails for more complicated scenarios
-        if not self._buffer and lines[:1] in [' ', '\t']:
+
+        if not self._buffer and lines[:1] in [' ', '\t'] and \
+           not comment_line_re.match(lines):
             lines = 'if 1:\n%s' % lines
         
         self._store(lines)
         source = self.source
 
         # Before calling _compile(), reset the code object to None so that if an
         # exception is raised in compilation, we don't mislead by having
         # inconsistent code/source attributes.
         self.code, self._is_complete = None, None
 
         self._update_indent(lines)
         try:
             self.code = self._compile(source)
         # Invalid syntax can produce any of a number of different errors from
         # inside the compiler, so we have to catch them all.  Syntax errors
         # immediately produce a 'ready' block, so the invalid Python can be
         # sent to the kernel for evaluation with possible ipython
         # special-syntax conversion.
         except (SyntaxError, OverflowError, ValueError, TypeError,
                 MemoryError):
             self._is_complete = True
         else:
             # Compilation didn't produce any exceptions (though it may not have
             # given a complete code object)
             self._is_complete = self.code is not None
 
         return self._is_complete
 
     def push_accepts_more(self):
         """Return whether a block of interactive input can accept more input.
 
         This method is meant to be used by line-oriented frontends, who need to
         guess whether a block is complete or not based solely on prior and
         current input lines.  The InputSplitter considers it has a complete
         interactive block and will not accept more input only when either a
         SyntaxError is raised, or *all* of the following are true:
 
         1. The input compiles to a complete statement.
         
         2. The indentation level is flush-left (because if we are indented,
            like inside a function definition or for loop, we need to keep
            reading new input).
           
         3. There is one extra line consisting only of whitespace.
 
         Because of condition #3, this method should be used only by
         *line-oriented* frontends, since it means that intermediate blank lines
         are not allowed in function definitions (or any other indented block).
 
         Block-oriented frontends that have a separate keyboard event to
         indicate execution should use the :meth:`split_blocks` method instead.
 
         If the current input produces a syntax error, this method immediately
         returns False but does *not* raise the syntax error exception, as
         typically clients will want to send invalid syntax to an execution
         backend which might convert the invalid syntax into valid Python via
         one of the dynamic IPython mechanisms.
         """
             
         if not self._is_complete:
             return True
 
         if self.indent_spaces==0:
             return False
         
         last_line = self.source.splitlines()[-1]
         return bool(last_line and not last_line.isspace())
         
     def split_blocks(self, lines):
         """Split a multiline string into multiple input blocks.
 
         Note: this method starts by performing a full reset().
         
         Parameters
         ----------
         lines : str
           A possibly multiline string.
 
         Returns
         -------
         blocks : list
           A list of strings, each possibly multiline.  Each string corresponds
           to a single block that can be compiled in 'single' mode (unless it
           has a syntax error)."""
 
         # This code is fairly delicate.  If you make any changes here, make
         # absolutely sure that you do run the full test suite and ALL tests
         # pass.
 
         self.reset()
         blocks = []
         
         # Reversed copy so we can use pop() efficiently and consume the input
         # as a stack
         lines = lines.splitlines()[::-1]
         # Outer loop over all input
         while lines:
             #print 'Current lines:', lines  # dbg
             # Inner loop to build each block
             while True:
                 # Safety exit from inner loop
                 if not lines:
                     break
                 # Grab next line but don't push it yet
                 next_line = lines.pop()
                 # Blank/empty lines are pushed as-is
                 if not next_line or next_line.isspace():
                     self.push(next_line)
                     continue
 
                 # Check indentation changes caused by the *next* line
                 indent_spaces, _full_dedent = self._find_indent(next_line)
 
                 # If the next line causes a dedent, it can be for two differnt
                 # reasons: either an explicit de-dent by the user or a
                 # return/raise/pass statement.  These MUST be handled
                 # separately:
                 #
                 # 1. the first case is only detected when the actual explicit
                 # dedent happens, and that would be the *first* line of a *new*
                 # block.  Thus, we must put the line back into the input buffer
                 # so that it starts a new block on the next pass.
                 #
                 # 2. the second case is detected in the line before the actual
                 # dedent happens, so , we consume the line and we can break out
                 # to start a new block.
 
                 # Case 1, explicit dedent causes a break.
                 # Note: check that we weren't on the very last line, else we'll
                 # enter an infinite loop adding/removing the last line.
                 if  _full_dedent and lines and not next_line.startswith(' '):
                     lines.append(next_line)
                     break
                 
                 # Otherwise any line is pushed
                 self.push(next_line)
 
                 # Case 2, full dedent with full block ready:
                 if _full_dedent or \
                        self.indent_spaces==0 and not self.push_accepts_more():
                     break
             # Form the new block with the current source input
             blocks.append(self.source_reset())
             
         #return blocks
         # HACK!!! Now that our input is in blocks but guaranteed to be pure
         # python syntax, feed it back a second time through the AST-based
         # splitter, which is more accurate than ours.
         return split_blocks(''.join(blocks))
 
     #------------------------------------------------------------------------
     # Private interface
     #------------------------------------------------------------------------
 
     def _find_indent(self, line):
         """Compute the new indentation level for a single line.
 
         Parameters
         ----------
         line : str
           A single new line of non-whitespace, non-comment Python input.
           
         Returns
         -------
         indent_spaces : int
           New value for the indent level (it may be equal to self.indent_spaces
         if indentation doesn't change.
 
         full_dedent : boolean
           Whether the new line causes a full flush-left dedent.
         """
         indent_spaces = self.indent_spaces
         full_dedent = self._full_dedent
         
         inisp = num_ini_spaces(line)
         if inisp < indent_spaces:
             indent_spaces = inisp
             if indent_spaces <= 0:
                 #print 'Full dedent in text',self.source # dbg
                 full_dedent = True
 
         if line[-1] == ':':
             indent_spaces += 4
         elif dedent_re.match(line):
             indent_spaces -= 4
             if indent_spaces <= 0:
                 full_dedent = True
 
         # Safety
         if indent_spaces < 0:
             indent_spaces = 0
             #print 'safety' # dbg
             
         return indent_spaces, full_dedent
         
     def _update_indent(self, lines):
         for line in remove_comments(lines).splitlines():
             if line and not line.isspace():
                 self.indent_spaces, self._full_dedent = self._find_indent(line)
 
     def _store(self, lines):
         """Store one or more lines of input.
 
         If input lines are not newline-terminated, a newline is automatically
         appended."""
 
         if lines.endswith('\n'):
             self._buffer.append(lines)
         else:
             self._buffer.append(lines+'\n')
         self._set_source()
 
     def _set_source(self):
         self.source = ''.join(self._buffer).encode(self.encoding)
 
 
 #-----------------------------------------------------------------------------
 # Functions and classes for IPython-specific syntactic support
 #-----------------------------------------------------------------------------
 
 # RegExp for splitting line contents into pre-char//first word-method//rest.
 # For clarity, each group in on one line.
 
 line_split = re.compile("""
              ^(\s*)              # any leading space
              ([,;/%]|!!?|\?\??)  # escape character or characters
              \s*(%?[\w\.]*)      # function/method, possibly with leading %
                                  # to correctly treat things like '?%magic'
              (\s+.*$|$)          # rest of line
              """, re.VERBOSE)
 
 
 def split_user_input(line):
     """Split user input into early whitespace, esc-char, function part and rest.
 
     This is currently handles lines with '=' in them in a very inconsistent
     manner.
 
     Examples
     ========
     >>> split_user_input('x=1')
     ('', '', 'x=1', '')
     >>> split_user_input('?')
     ('', '?', '', '')
     >>> split_user_input('??')
     ('', '??', '', '')
     >>> split_user_input(' ?')
     (' ', '?', '', '')
     >>> split_user_input(' ??')
     (' ', '??', '', '')
     >>> split_user_input('??x')
     ('', '??', 'x', '')
     >>> split_user_input('?x=1')
     ('', '', '?x=1', '')
     >>> split_user_input('!ls')
     ('', '!', 'ls', '')
     >>> split_user_input('  !ls')
     ('  ', '!', 'ls', '')
     >>> split_user_input('!!ls')
     ('', '!!', 'ls', '')
     >>> split_user_input('  !!ls')
     ('  ', '!!', 'ls', '')
     >>> split_user_input(',ls')
     ('', ',', 'ls', '')
     >>> split_user_input(';ls')
     ('', ';', 'ls', '')
     >>> split_user_input('  ;ls')
     ('  ', ';', 'ls', '')
     >>> split_user_input('f.g(x)')
     ('', '', 'f.g(x)', '')
     >>> split_user_input('f.g (x)')
     ('', '', 'f.g', '(x)')
     >>> split_user_input('?%hist')
     ('', '?', '%hist', '')
     """
     match = line_split.match(line)
     if match:
         lspace, esc, fpart, rest = match.groups()
     else:
         # print "match failed for line '%s'" % line
         try:
             fpart, rest = line.split(None, 1)
         except ValueError:
             # print "split failed for line '%s'" % line
             fpart, rest = line,''
         lspace = re.match('^(\s*)(.*)', line).groups()[0]
         esc = ''
 
     # fpart has to be a valid python identifier, so it better be only pure
     # ascii, no unicode:
     try:
         fpart = fpart.encode('ascii')
     except UnicodeEncodeError:
         lspace = unicode(lspace)
         rest = fpart + u' ' + rest
         fpart = u''
 
     #print 'line:<%s>' % line # dbg
     #print 'esc <%s> fpart <%s> rest <%s>' % (esc,fpart.strip(),rest) # dbg
     return lspace, esc, fpart.strip(), rest.lstrip()
 
 
 # The escaped translators ALL receive a line where their own escape has been
 # stripped.  Only '?' is valid at the end of the line, all others can only be
 # placed at the start.
 
 class LineInfo(object):
     """A single line of input and associated info.
 
     This is a utility class that mostly wraps the output of
     :func:`split_user_input` into a convenient object to be passed around
     during input transformations.
 
     Includes the following as properties: 
 
     line
       The original, raw line
 
     lspace
       Any early whitespace before actual text starts.
 
     esc
       The initial esc character (or characters, for double-char escapes like
       '??' or '!!').
     
     fpart
       The 'function part', which is basically the maximal initial sequence
       of valid python identifiers and the '.' character.  This is what is
       checked for alias and magic transformations, used for auto-calling,
       etc.
     
     rest
       Everything else on the line.
     """
     def __init__(self, line):
         self.line = line
         self.lspace, self.esc, self.fpart, self.rest = \
                              split_user_input(line)
 
     def __str__(self):                                                         
         return "LineInfo [%s|%s|%s|%s]" % (self.lspace, self.esc,
                                            self.fpart, self.rest)
 
 
 # Transformations of the special syntaxes that don't rely on an explicit escape
 # character but instead on patterns on the input line
 
 # The core transformations are implemented as standalone functions that can be
 # tested and validated in isolation.  Each of these uses a regexp, we
 # pre-compile these and keep them close to each function definition for clarity
 
 _assign_system_re = re.compile(r'(?P<lhs>(\s*)([\w\.]+)((\s*,\s*[\w\.]+)*))'
                                r'\s*=\s*!\s*(?P<cmd>.*)')
 
 def transform_assign_system(line):
     """Handle the `files = !ls` syntax."""
     # FIXME: This transforms the line to use %sc, but we've listed that magic
     # as deprecated.  We should then implement this functionality in a
     # standalone api that we can transform to, without going through a
     # deprecated magic.
     m = _assign_system_re.match(line)
     if m is not None:
         cmd = m.group('cmd')
         lhs = m.group('lhs')
         expr = make_quoted_expr("sc -l = %s" % cmd)
         new_line = '%s = get_ipython().magic(%s)' % (lhs, expr)
         return new_line
     return line
 
 
 _assign_magic_re = re.compile(r'(?P<lhs>(\s*)([\w\.]+)((\s*,\s*[\w\.]+)*))'
                                r'\s*=\s*%\s*(?P<cmd>.*)')
 
 def transform_assign_magic(line):
     """Handle the `a = %who` syntax."""
     m = _assign_magic_re.match(line)
     if m is not None:
         cmd = m.group('cmd')
         lhs = m.group('lhs')
         expr = make_quoted_expr(cmd)
         new_line = '%s = get_ipython().magic(%s)' % (lhs, expr)
         return new_line
     return line
 
 
 _classic_prompt_re = re.compile(r'^([ \t]*>>> |^[ \t]*\.\.\. )')
 
 def transform_classic_prompt(line):
     """Handle inputs that start with '>>> ' syntax."""
 
     if not line or line.isspace():
         return line
     m = _classic_prompt_re.match(line)
     if m:
         return line[len(m.group(0)):]
     else:
         return line
 
 
 _ipy_prompt_re = re.compile(r'^([ \t]*In \[\d+\]: |^[ \t]*\ \ \ \.\.\.+: )')
 
 def transform_ipy_prompt(line):
     """Handle inputs that start classic IPython prompt syntax."""
 
     if not line or line.isspace():
         return line
     #print 'LINE:  %r' % line # dbg
     m = _ipy_prompt_re.match(line)
     if m:
         #print 'MATCH! %r -> %r' % (line, line[len(m.group(0)):]) # dbg
         return line[len(m.group(0)):]
     else:
         return line
 
 
 class EscapedTransformer(object):
     """Class to transform lines that are explicitly escaped out."""
 
     def __init__(self):
         tr = { ESC_SHELL  : self._tr_system,
                ESC_SH_CAP : self._tr_system2,
                ESC_HELP   : self._tr_help,
                ESC_HELP2  : self._tr_help,
                ESC_MAGIC  : self._tr_magic,
                ESC_QUOTE  : self._tr_quote,
                ESC_QUOTE2 : self._tr_quote2,
                ESC_PAREN  : self._tr_paren }
         self.tr = tr
         
     # Support for syntax transformations that use explicit escapes typed by the
     # user at the beginning of a line
     @staticmethod
     def _tr_system(line_info):
         "Translate lines escaped with: !"
         cmd = line_info.line.lstrip().lstrip(ESC_SHELL)
         return '%sget_ipython().system(%s)' % (line_info.lspace,
                                                make_quoted_expr(cmd))
 
     @staticmethod
     def _tr_system2(line_info):
         "Translate lines escaped with: !!"
         cmd = line_info.line.lstrip()[2:]
         return '%sget_ipython().getoutput(%s)' % (line_info.lspace,
                                                   make_quoted_expr(cmd))
 
     @staticmethod
     def _tr_help(line_info):
         "Translate lines escaped with: ?/??"
         # A naked help line should just fire the intro help screen
         if not line_info.line[1:]:
             return 'get_ipython().show_usage()'
 
         # There may be one or two '?' at the end, move them to the front so that
         # the rest of the logic can assume escapes are at the start
         line = line_info.line
         if line.endswith('?'):
             line = line[-1] + line[:-1]
         if line.endswith('?'):
             line = line[-1] + line[:-1]
         line_info = LineInfo(line)
 
         # From here on, simply choose which level of detail to get.
         if line_info.esc == '?':
             pinfo = 'pinfo'
         elif line_info.esc == '??':
             pinfo = 'pinfo2'
 
         tpl = '%sget_ipython().magic("%s %s")'
         return tpl % (line_info.lspace, pinfo,
                       ' '.join([line_info.fpart, line_info.rest]).strip())
 
     @staticmethod
     def _tr_magic(line_info):
         "Translate lines escaped with: %"
         tpl = '%sget_ipython().magic(%s)'
         cmd = make_quoted_expr(' '.join([line_info.fpart,
                                          line_info.rest]).strip())
         return tpl % (line_info.lspace, cmd)
 
     @staticmethod
     def _tr_quote(line_info):
         "Translate lines escaped with: ,"
         return '%s%s("%s")' % (line_info.lspace, line_info.fpart,
                              '", "'.join(line_info.rest.split()) )
 
     @staticmethod
     def _tr_quote2(line_info):
         "Translate lines escaped with: ;"
         return '%s%s("%s")' % (line_info.lspace, line_info.fpart,
                                line_info.rest)
 
     @staticmethod
     def _tr_paren(line_info):
         "Translate lines escaped with: /"
         return '%s%s(%s)' % (line_info.lspace, line_info.fpart,
                              ", ".join(line_info.rest.split()))
 
     def __call__(self, line):
         """Class to transform lines that are explicitly escaped out.
 
         This calls the above _tr_* static methods for the actual line
         translations."""
 
         # Empty lines just get returned unmodified
         if not line or line.isspace():
             return line
 
         # Get line endpoints, where the escapes can be
         line_info = LineInfo(line)
 
         # If the escape is not at the start, only '?' needs to be special-cased.
         # All other escapes are only valid at the start
         if not line_info.esc in self.tr:
             if line.endswith(ESC_HELP):
                 return self._tr_help(line_info)
             else:
                 # If we don't recognize the escape, don't modify the line
                 return line
 
         return self.tr[line_info.esc](line_info)
 
 
 # A function-looking object to be used by the rest of the code.  The purpose of
 # the class in this case is to organize related functionality, more than to
 # manage state.
 transform_escaped = EscapedTransformer()
 
 
 class IPythonInputSplitter(InputSplitter):
     """An input splitter that recognizes all of IPython's special syntax."""
 
     def push(self, lines):
         """Push one or more lines of IPython input.
         """
         if not lines:
             return super(IPythonInputSplitter, self).push(lines)
 
         lines_list = lines.splitlines()
 
         transforms = [transform_escaped, transform_assign_system,
                       transform_assign_magic, transform_ipy_prompt,
                       transform_classic_prompt]
 
         # Transform logic
         #
         # We only apply the line transformers to the input if we have either no
         # input yet, or complete input, or if the last line of the buffer ends
         # with ':' (opening an indented block).  This prevents the accidental
         # transformation of escapes inside multiline expressions like
         # triple-quoted strings or parenthesized expressions.
         #
         # The last heuristic, while ugly, ensures that the first line of an
         # indented block is correctly transformed.
         #
         # FIXME: try to find a cleaner approach for this last bit.
 
         # If we were in 'block' mode, since we're going to pump the parent
         # class by hand line by line, we need to temporarily switch out to
         # 'line' mode, do a single manual reset and then feed the lines one
         # by one.  Note that this only matters if the input has more than one
         # line.
         changed_input_mode = False
         
         if len(lines_list)>1 and self.input_mode == 'block':
             self.reset()
             changed_input_mode = True
             saved_input_mode = 'block'
             self.input_mode = 'line'
 
         try:
             push = super(IPythonInputSplitter, self).push
             for line in lines_list:
                 if self._is_complete or not self._buffer or \
                    (self._buffer and self._buffer[-1].rstrip().endswith(':')):
                     for f in transforms:
                         line = f(line)
 
                 out = push(line)
         finally:
             if changed_input_mode:
                 self.input_mode = saved_input_mode
         
         return out