Expand a bit the documentation about transformers.

Mostly answering questions I had myself while trying to write some stuff
and while trying to get a simple example working.

IPython/core/inputsplitter.py

@@ -1,743 +1,741 b''
 """Input handling and transformation machinery.
 
 The first class in this module, :class:`InputSplitter`, is designed to tell when
 input from a line-oriented frontend is complete and should be executed, and when
 the user should be prompted for another line of code instead. The name 'input
 splitter' is largely for historical reasons.
 
 A companion, :class:`IPythonInputSplitter`, provides the same functionality but
 with full support for the extended IPython syntax (magics, system calls, etc).
 The code to actually do these transformations is in :mod:`IPython.core.inputtransformer`.
 :class:`IPythonInputSplitter` feeds the raw code to the transformers in order
 and stores the results.
 
 For more details, see the class docstrings below.
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 import ast
 import codeop
 import io
 import re
 import sys
 import tokenize
 import warnings
 
-from IPython.utils.py3compat import cast_unicode
 from IPython.core.inputtransformer import (leading_indent,
                                            classic_prompt,
                                            ipy_prompt,
                                            cellmagic,
                                            assemble_logical_lines,
                                            help_end,
                                            escaped_commands,
                                            assign_from_magic,
                                            assign_from_system,
                                            assemble_python_lines,
                                            )
 
 # These are available in this module for backwards compatibility.
 from IPython.core.inputtransformer import (ESC_SHELL, ESC_SH_CAP, ESC_HELP,
                                         ESC_HELP2, ESC_MAGIC, ESC_MAGIC2,
                                         ESC_QUOTE, ESC_QUOTE2, ESC_PAREN, ESC_SEQUENCES)
 
 #-----------------------------------------------------------------------------
 # 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('|'.join([
     r'^\s+raise(\s.*)?$', # raise statement (+ space + other stuff, maybe)
     r'^\s+raise\([^\)]*\).*$', # wacky raise with immediate open paren
     r'^\s+return(\s.*)?$', # normal return (+ space + other stuff, maybe)
     r'^\s+return\([^\)]*\).*$', # wacky return with immediate open paren
     r'^\s+pass\s*$', # pass (optionally followed by trailing spaces)
     r'^\s+break\s*$', # break (optionally followed by trailing spaces)
     r'^\s+continue\s*$', # continue (optionally followed by trailing spaces)
 ]))
 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
 
 # Fake token types for partial_tokenize:
 INCOMPLETE_STRING = tokenize.N_TOKENS
 IN_MULTILINE_STATEMENT = tokenize.N_TOKENS + 1
 
 # The 2 classes below have the same API as TokenInfo, but don't try to look up
 # a token type name that they won't find.
 class IncompleteString:
     type = exact_type = INCOMPLETE_STRING
     def __init__(self, s, start, end, line):
         self.s = s
         self.start = start
         self.end = end
         self.line = line
 
 class InMultilineStatement:
     type = exact_type = IN_MULTILINE_STATEMENT
     def __init__(self, pos, line):
         self.s = ''
         self.start = self.end = pos
         self.line = line
 
 def partial_tokens(s):
     """Iterate over tokens from a possibly-incomplete string of code.
 
     This adds two special token types: INCOMPLETE_STRING and
     IN_MULTILINE_STATEMENT. These can only occur as the last token yielded, and
     represent the two main ways for code to be incomplete.
     """
     readline = io.StringIO(s).readline
     token = tokenize.TokenInfo(tokenize.NEWLINE, '', (1, 0), (1, 0), '')
     try:
         for token in tokenize.generate_tokens(readline):
             yield token
     except tokenize.TokenError as e:
         # catch EOF error
         lines = s.splitlines(keepends=True)
         end = len(lines), len(lines[-1])
         if 'multi-line string' in e.args[0]:
             l, c = start = token.end
             s = lines[l-1][c:] + ''.join(lines[l:])
             yield IncompleteString(s, start, end, lines[-1])
         elif 'multi-line statement' in e.args[0]:
             yield InMultilineStatement(end, lines[-1])
         else:
             raise
 
 def find_next_indent(code):
     """Find the number of spaces for the next line of indentation"""
     tokens = list(partial_tokens(code))
     if tokens[-1].type == tokenize.ENDMARKER:
         tokens.pop()
     if not tokens:
         return 0
     while (tokens[-1].type in {tokenize.DEDENT, tokenize.NEWLINE, tokenize.COMMENT}):
         tokens.pop()
 
     if tokens[-1].type == INCOMPLETE_STRING:
         # Inside a multiline string
         return 0
 
     # Find the indents used before
     prev_indents = [0]
     def _add_indent(n):
         if n != prev_indents[-1]:
             prev_indents.append(n)
 
     tokiter = iter(tokens)
     for tok in tokiter:
         if tok.type in {tokenize.INDENT, tokenize.DEDENT}:
             _add_indent(tok.end[1])
         elif (tok.type == tokenize.NL):
             try:
                 _add_indent(next(tokiter).start[1])
             except StopIteration:
                 break
 
     last_indent = prev_indents.pop()
 
     # If we've just opened a multiline statement (e.g. 'a = ['), indent more
     if tokens[-1].type == IN_MULTILINE_STATEMENT:
         if tokens[-2].exact_type in {tokenize.LPAR, tokenize.LSQB, tokenize.LBRACE}:
             return last_indent + 4
         return last_indent
 
     if tokens[-1].exact_type == tokenize.COLON:
         # Line ends with colon - indent
         return last_indent + 4
 
     if last_indent:
         # Examine the last line for dedent cues - statements like return or
         # raise which normally end a block of code.
         last_line_starts = 0
         for i, tok in enumerate(tokens):
             if tok.type == tokenize.NEWLINE:
                 last_line_starts = i + 1
 
         last_line_tokens = tokens[last_line_starts:]
         names = [t.string for t in last_line_tokens if t.type == tokenize.NAME]
         if names and names[0] in {'raise', 'return', 'pass', 'break', 'continue'}:
             # Find the most recent indentation less than the current level
             for indent in reversed(prev_indents):
                 if indent < last_indent:
                     return indent
 
     return last_indent
 
 
 def last_blank(src):
     """Determine if the input source ends in a blank.
 
     A blank is either a newline or a line consisting of whitespace.
 
     Parameters
     ----------
     src : string
       A single or multiline string.
     """
     if not src: return False
     ll  = src.splitlines()[-1]
     return (ll == '') or ll.isspace()
 
 
 last_two_blanks_re = re.compile(r'\n\s*\n\s*$', re.MULTILINE)
 last_two_blanks_re2 = re.compile(r'.+\n\s*\n\s+$', re.MULTILINE)
 
 def last_two_blanks(src):
     """Determine if the input source ends in two blanks.
 
     A blank is either a newline or a line consisting of whitespace.
 
     Parameters
     ----------
     src : string
       A single or multiline string.
     """
     if not src: return False
     # The logic here is tricky: I couldn't get a regexp to work and pass all
     # the tests, so I took a different approach: split the source by lines,
     # grab the last two and prepend '###\n' as a stand-in for whatever was in
     # the body before the last two lines.  Then, with that structure, it's
     # possible to analyze with two regexps.  Not the most elegant solution, but
     # it works.  If anyone tries to change this logic, make sure to validate
     # the whole test suite first!
     new_src = '\n'.join(['###\n'] + src.splitlines()[-2:])
     return (bool(last_two_blanks_re.match(new_src)) or
             bool(last_two_blanks_re2.match(new_src)) )
 
 
 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
 #-----------------------------------------------------------------------------
 
 class InputSplitter(object):
     r"""An object that can accumulate lines of Python source before execution.
 
     This object is designed to be fed python source line-by-line, using
     :meth:`push`. 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.
 
     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
 
     # 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
     # Boolean indicating whether the current block has an unrecoverable syntax error
     _is_invalid = False
 
     def __init__(self):
         """Create a new InputSplitter instance.
         """
         self._buffer = []
         self._compile = codeop.CommandCompiler()
         self.encoding = get_input_encoding()
 
     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._is_invalid = 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 check_complete(self, source):
         """Return whether a block of code is ready to execute, or should be continued
         
         This is a non-stateful API, and will reset the state of this InputSplitter.
         
         Parameters
         ----------
         source : string
           Python input code, which can be multiline.
         
         Returns
         -------
         status : str
           One of 'complete', 'incomplete', or 'invalid' if source is not a
           prefix of valid code.
         indent_spaces : int or None
           The number of spaces by which to indent the next line of code. If
           status is not 'incomplete', this is None.
         """
         self.reset()
         try:
             self.push(source)
         except SyntaxError:
             # Transformers in IPythonInputSplitter can raise SyntaxError,
             # which push() will not catch.
             return 'invalid', None
         else:
             if self._is_invalid:
                 return 'invalid', None
             elif self.push_accepts_more():
                 return 'incomplete', self.indent_spaces
             else:
                 return 'complete', None
         finally:
             self.reset()
 
     def push(self, lines):
         """Push one or 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.
         """
         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._is_invalid = False
 
         # Honor termination lines properly
         if source.endswith('\\\n'):
             return False
 
         self._update_indent()
         try:
             with warnings.catch_warnings():
                 warnings.simplefilter('error', SyntaxWarning)
                 self.code = self._compile(source, symbol="exec")
         # 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, SyntaxWarning):
             self._is_complete = True
             self._is_invalid = 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 when either:
         
         * A SyntaxError is raised
 
         * The code is complete and consists of a single line or a single
           non-compound statement
 
         * The code is complete and has a blank line at the end
 
         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.
         """
 
         # With incomplete input, unconditionally accept more
         # A syntax error also sets _is_complete to True - see push()
         if not self._is_complete:
             #print("Not complete")  # debug
             return True
         
         # The user can make any (complete) input execute by leaving a blank line
         last_line = self.source.splitlines()[-1]
         if (not last_line) or last_line.isspace():
             #print("Blank line")  # debug
             return False
         
         # If there's just a single line or AST node, and we're flush left, as is
         # the case after a simple statement such as 'a=1', we want to execute it
         # straight away.
         if self.indent_spaces==0:
             if len(self.source.splitlines()) <= 1:
                 return False
             
             try:
                 code_ast = ast.parse(u''.join(self._buffer))
             except Exception:
                 #print("Can't parse AST")  # debug
                 return False
             else:
                 if len(code_ast.body) == 1 and \
                                     not hasattr(code_ast.body[0], 'body'):
                     #print("Simple statement")  # debug
                     return False
 
         # General fallback - accept more code
         return True
 
     def _update_indent(self):
         # self.source always has a trailing newline
         self.indent_spaces = find_next_indent(self.source[:-1])
         self._full_dedent = (self.indent_spaces == 0)
 
     def _store(self, lines, buffer=None, store='source'):
         """Store one or more lines of input.
 
         If input lines are not newline-terminated, a newline is automatically
         appended."""
 
         if buffer is None:
             buffer = self._buffer
 
         if lines.endswith('\n'):
             buffer.append(lines)
         else:
             buffer.append(lines+'\n')
         setattr(self, store, self._set_source(buffer))
 
     def _set_source(self, buffer):
         return u''.join(buffer)
 
 
 class IPythonInputSplitter(InputSplitter):
     """An input splitter that recognizes all of IPython's special syntax."""
 
     # String with raw, untransformed input.
     source_raw = ''
     
     # Flag to track when a transformer has stored input that it hasn't given
     # back yet.
     transformer_accumulating = False
     
     # Flag to track when assemble_python_lines has stored input that it hasn't
     # given back yet.
     within_python_line = False
 
     # Private attributes
 
     # List with lines of raw input accumulated so far.
     _buffer_raw = None
 
     def __init__(self, line_input_checker=True, physical_line_transforms=None,
                     logical_line_transforms=None, python_line_transforms=None):
         super(IPythonInputSplitter, self).__init__()
         self._buffer_raw = []
         self._validate = True
         
         if physical_line_transforms is not None:
             self.physical_line_transforms = physical_line_transforms
         else:
             self.physical_line_transforms = [
                                              leading_indent(),
                                              classic_prompt(),
                                              ipy_prompt(),
                                              cellmagic(end_on_blank_line=line_input_checker),
                                             ]
         
         self.assemble_logical_lines = assemble_logical_lines()
         if logical_line_transforms is not None:
             self.logical_line_transforms = logical_line_transforms
         else:
             self.logical_line_transforms = [
                                             help_end(),
                                             escaped_commands(),
                                             assign_from_magic(),
                                             assign_from_system(),
                                            ]
         
         self.assemble_python_lines = assemble_python_lines()
         if python_line_transforms is not None:
             self.python_line_transforms = python_line_transforms
         else:
             # We don't use any of these at present
             self.python_line_transforms = []
     
     @property
     def transforms(self):
         "Quick access to all transformers."
         return self.physical_line_transforms + \
             [self.assemble_logical_lines] + self.logical_line_transforms + \
             [self.assemble_python_lines]  + self.python_line_transforms
     
     @property
     def transforms_in_use(self):
         """Transformers, excluding logical line transformers if we're in a
         Python line."""
         t = self.physical_line_transforms[:]
         if not self.within_python_line:
             t += [self.assemble_logical_lines] + self.logical_line_transforms
         return t + [self.assemble_python_lines] + self.python_line_transforms
 
     def reset(self):
         """Reset the input buffer and associated state."""
         super(IPythonInputSplitter, self).reset()
         self._buffer_raw[:] = []
         self.source_raw = ''
         self.transformer_accumulating = False
         self.within_python_line = False
 
         for t in self.transforms:
             try:
                 t.reset()
             except SyntaxError:
                 # Nothing that calls reset() expects to handle transformer
                 # errors
                 pass
     
     def flush_transformers(self):
         def _flush(transform, outs):
             """yield transformed lines
             
             always strings, never None
             
             transform: the current transform
             outs: an iterable of previously transformed inputs.
                  Each may be multiline, which will be passed
                  one line at a time to transform.
             """
             for out in outs:
                 for line in out.splitlines():
                     # push one line at a time
                     tmp = transform.push(line)
                     if tmp is not None:
                         yield tmp
             
             # reset the transform
             tmp = transform.reset()
             if tmp is not None:
                 yield tmp
         
         out = []
         for t in self.transforms_in_use:
             out = _flush(t, out)
         
         out = list(out)
         if out:
             self._store('\n'.join(out))
 
     def raw_reset(self):
         """Return raw input only and perform a full reset.
         """
         out = self.source_raw
         self.reset()
         return out
     
     def source_reset(self):
         try:
             self.flush_transformers()
             return self.source
         finally:
             self.reset()
 
     def push_accepts_more(self):
         if self.transformer_accumulating:
             return True
         else:
             return super(IPythonInputSplitter, self).push_accepts_more()
 
     def transform_cell(self, cell):
         """Process and translate a cell of input.
         """
         self.reset()
         try:
             self.push(cell)
             self.flush_transformers()
             return self.source
         finally:
             self.reset()
 
     def push(self, lines):
         """Push one or more lines of IPython input.
 
         This stores the given lines and returns a status code indicating
         whether the code forms a complete Python block or not, after processing
         all input lines for special IPython syntax.
 
         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.
         """
 
         # We must ensure all input is pure unicode
-        lines = cast_unicode(lines, self.encoding)
         # ''.splitlines() --> [], but we need to push the empty line to transformers
         lines_list = lines.splitlines()
         if not lines_list:
             lines_list = ['']
 
         # Store raw source before applying any transformations to it.  Note
         # that this must be done *after* the reset() call that would otherwise
         # flush the buffer.
         self._store(lines, self._buffer_raw, 'source_raw')
 
         for line in lines_list:
             out = self.push_line(line)
 
         return out
     
     def push_line(self, line):
         buf = self._buffer
         
         def _accumulating(dbg):
             #print(dbg)
             self.transformer_accumulating = True
             return False
         
         for transformer in self.physical_line_transforms:
             line = transformer.push(line)
             if line is None:
                 return _accumulating(transformer)
         
         if not self.within_python_line:
             line = self.assemble_logical_lines.push(line)
             if line is None:
                 return _accumulating('acc logical line')        
         
             for transformer in self.logical_line_transforms:
                 line = transformer.push(line)
                 if line is None:
                     return _accumulating(transformer)
         
         line = self.assemble_python_lines.push(line)
         if line is None:
             self.within_python_line = True
             return _accumulating('acc python line')
         else:
             self.within_python_line = False
         
         for transformer in self.python_line_transforms:
             line = transformer.push(line)
             if line is None:
                 return _accumulating(transformer)
 
         #print("transformers clear") #debug
         self.transformer_accumulating = False
         return super(IPythonInputSplitter, self).push(line)

docs/source/config/inputtransforms.rst

@@ -1,139 +1,184 b''
 
 ===========================
 Custom input transformation
 ===========================
 
 IPython extends Python syntax to allow things like magic commands, and help with
 the ``?`` syntax. There are several ways to customise how the user's input is
 processed into Python code to be executed.
 
 These hooks are mainly for other projects using IPython as the core of their
 interactive interface. Using them carelessly can easily break IPython!
 
 String based transformations
 ============================
 
 .. currentmodule:: IPython.core.inputtransforms
 
 When the user enters a line of code, it is first processed as a string. By the
 end of this stage, it must be valid Python syntax.
 
 These transformers all subclass :class:`IPython.core.inputtransformer.InputTransformer`,
 and are used by :class:`IPython.core.inputsplitter.IPythonInputSplitter`.
 
 These transformers act in three groups, stored separately as lists of instances
 in attributes of :class:`~IPython.core.inputsplitter.IPythonInputSplitter`:
 
 * ``physical_line_transforms`` act on the lines as the user enters them. For
   example, these strip Python prompts from examples pasted in.
 * ``logical_line_transforms`` act on lines as connected by explicit line
   continuations, i.e. ``\`` at the end of physical lines. They are skipped
   inside multiline Python statements. This is the point where IPython recognises
   ``%magic`` commands, for instance.
 * ``python_line_transforms`` act on blocks containing complete Python statements.
   Multi-line strings, lists and function calls are reassembled before being
   passed to these, but note that function and class *definitions* are still a
   series of separate statements. IPython does not use any of these by default.
 
 An InteractiveShell instance actually has two
 :class:`~IPython.core.inputsplitter.IPythonInputSplitter` instances, as the
 attributes :attr:`~IPython.core.interactiveshell.InteractiveShell.input_splitter`,
 to tell when a block of input is complete, and
 :attr:`~IPython.core.interactiveshell.InteractiveShell.input_transformer_manager`,
 to transform complete cells. If you add a transformer, you should make sure that
 it gets added to both, e.g.::
 
     ip.input_splitter.logical_line_transforms.append(my_transformer())
     ip.input_transformer_manager.logical_line_transforms.append(my_transformer())
 
 These transformers may raise :exc:`SyntaxError` if the input code is invalid, but
 in most cases it is clearer to pass unrecognised code through unmodified and let
 Python's own parser decide whether it is valid.
 
 .. versionchanged:: 2.0
 
    Added the option to raise :exc:`SyntaxError`.
 
 Stateless transformations
 -------------------------
 
 The simplest kind of transformations work one line at a time. Write a function
 which takes a line and returns a line, and decorate it with
 :meth:`StatelessInputTransformer.wrap`::
 
     @StatelessInputTransformer.wrap
     def my_special_commands(line):
         if line.startswith("¬"):
             return "specialcommand(" + repr(line) + ")"
         return line
 
 The decorator returns a factory function which will produce instances of
 :class:`~IPython.core.inputtransformer.StatelessInputTransformer` using your
 function.
 
+Transforming a full block
+-------------------------
+
+Transforming a full block of python code is possible by implementing a
+:class:`~IPython.core.inputtransformer.Inputtransformer` and overwriting the
+``push`` and ``reset`` methods. The reset method should send the full block of
+transformed text. As an example a transformer the reversed the lines from last
+to first.
+
+    from IPython.core.inputtransformer import InputTransformer
+
+    class ReverseLineTransformer(InputTransformer):
+
+        def __init__(self):
+            self.acc = []
+
+        def push(self, line):
+            self.acc.append(line)
+            return None
+
+        def reset(self):
+            ret = '\n'.join(self.acc[::-1])
+            self.acc = []
+            return ret
+
+
 Coroutine transformers
 ----------------------
 
 More advanced transformers can be written as coroutines. The coroutine will be
 sent each line in turn, followed by ``None`` to reset it. It can yield lines, or
 ``None`` if it is accumulating text to yield at a later point. When reset, it
 should give up any code it has accumulated.
 
+You may use :meth:`CoroutineInputTransformer.wrap` to simplify the creation of
+such a transformer.
+
+Here is a simple :class:`CoroutineInputTransformer` that can be though of be
+being the identity::
+
+    @CoroutineInputTransformer.wrap
+    def noop():
+        line = ''
+        while True:
+            line = (yield line)
+
+    ip = get_ipython()
+
+    ip.input_splitter.logical_line_transforms.append(noop())
+    ip.input_transformer_manager.logical_line_transforms.append(noop())
+
 This code in IPython strips a constant amount of leading indentation from each
 line in a cell::
 
+    from IPython.core.inputtransformer import CoroutineInputTransformer
+
     @CoroutineInputTransformer.wrap
     def leading_indent():
         """Remove leading indentation.
         
         If the first line starts with a spaces or tabs, the same whitespace will be
         removed from each following line until it is reset.
         """
         space_re = re.compile(r'^[ \t]+')
         line = ''
         while True:
             line = (yield line)
             
             if line is None:
                 continue
             
             m = space_re.match(line)
             if m:
                 space = m.group(0)
                 while line is not None:
                     if line.startswith(space):
                         line = line[len(space):]
                     line = (yield line)
             else:
                 # No leading spaces - wait for reset
                 while line is not None:
                     line = (yield line)
 
 
 Token-based transformers
 ------------------------
 
 There is an experimental framework that takes care of tokenizing and
 untokenizing lines of code. Define a function that accepts a list of tokens, and
 returns an iterable of output tokens, and decorate it with
 :meth:`TokenInputTransformer.wrap`. These should only be used in
 ``python_line_transforms``.
 
 AST transformations
 ===================
 
 After the code has been parsed as Python syntax, you can use Python's powerful
 *Abstract Syntax Tree* tools to modify it. Subclass :class:`ast.NodeTransformer`,
 and add an instance to ``shell.ast_transformers``.
 
 This example wraps integer literals in an ``Integer`` class, which is useful for
 mathematical frameworks that want to handle e.g. ``1/3`` as a precise fraction::
 
 
     class IntegerWrapper(ast.NodeTransformer):
         """Wraps all integers in a call to Integer()"""
         def visit_Num(self, node):
             if isinstance(node.n, int):
                 return ast.Call(func=ast.Name(id='Integer', ctx=ast.Load()),
                                 args=[node], keywords=[])
             return node