Transformers have been added to the prefilter.

Transformers are run first before the checkers/handlers and
simple transform lines of input.  In the long run, we are going
to move away from checkers/handlers and just use transformers.

The new transformers are used to implement the a=!ls and b=%who
syntax.

IPython/core/prefilter.py

@@ -1,836 +1,995 b''
 #!/usr/bin/env python
 # encoding: utf-8
 """
 Prefiltering components.
 
+Prefilters transform user input before it is exec'd by Python.  These
+transforms are used to implement additional syntax such as !ls and %magic.
+
 Authors:
 
 * Brian Granger
 * Fernando Perez
 * Dan Milstein
+* Ville Vainio
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2009  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
 #-----------------------------------------------------------------------------
 
 import __builtin__
 import codeop
 import keyword
 import os
 import re
 import sys
 
 from IPython.core.alias import AliasManager
 from IPython.core.autocall import IPyAutocall
 from IPython.core.component import Component
 from IPython.core.splitinput import split_user_input
 from IPython.core.page import page
 
-from IPython.utils.traitlets import List, Int, Any, Str, CBool
+from IPython.utils.traitlets import List, Int, Any, Str, CBool, Bool
 from IPython.utils.genutils import make_quoted_expr
 from IPython.utils.autoattr import auto_attr
 
 #-----------------------------------------------------------------------------
 # Global utilities, errors and constants
 #-----------------------------------------------------------------------------
 
 # Warning, these cannot be changed unless various regular expressions
 # are updated in a number of places.  Not great, but at least we told you.
 ESC_SHELL  = '!'
 ESC_SH_CAP = '!!'
 ESC_HELP   = '?'
 ESC_MAGIC  = '%'
 ESC_QUOTE  = ','
 ESC_QUOTE2 = ';'
 ESC_PAREN  = '/'
 
 
 class PrefilterError(Exception):
     pass
 
 
 # RegExp to identify potential function names
 re_fun_name = re.compile(r'[a-zA-Z_]([a-zA-Z0-9_.]*) *$')
 
 # RegExp to exclude strings with this start from autocalling.  In
 # particular, all binary operators should be excluded, so that if foo is
 # callable, foo OP bar doesn't become foo(OP bar), which is invalid.  The
 # characters '!=()' don't need to be checked for, as the checkPythonChars
 # routine explicitely does so, to catch direct calls and rebindings of
 # existing names.
 
 # Warning: the '-' HAS TO BE AT THE END of the first group, otherwise
 # it affects the rest of the group in square brackets.
 re_exclude_auto = re.compile(r'^[,&^\|\*/\+-]'
                              r'|^is |^not |^in |^and |^or ')
 
 # try to catch also methods for stuff in lists/tuples/dicts: off
 # (experimental). For this to work, the line_split regexp would need
 # to be modified so it wouldn't break things at '['. That line is
 # nasty enough that I shouldn't change it until I can test it _well_.
 #self.re_fun_name = re.compile (r'[a-zA-Z_]([a-zA-Z0-9_.\[\]]*) ?$')
 
 
 # Handler Check Utilities
 def is_shadowed(identifier, ip):
     """Is the given identifier defined in one of the namespaces which shadow
     the alias and magic namespaces?  Note that an identifier is different
     than ifun, because it can not contain a '.' character."""
     # This is much safer than calling ofind, which can change state
     return (identifier in ip.user_ns \
             or identifier in ip.internal_ns \
             or identifier in ip.ns_table['builtin'])
 
 
 #-----------------------------------------------------------------------------
 # The LineInfo class used throughout
 #-----------------------------------------------------------------------------
 
 
 class LineInfo(object):
     """A single line of input and associated info.
 
     Includes the following as properties: 
 
     line
       The original, raw line
     
     continue_prompt
       Is this line a continuation in a sequence of multiline input?
     
     pre
       The initial esc character or whitespace.
     
     pre_char
       The escape character(s) in pre or the empty string if there isn't one.
       Note that '!!' is a possible value for pre_char.  Otherwise it will
       always be a single character.
     
     pre_whitespace
       The leading whitespace from pre if it exists.  If there is a pre_char,
       this is just ''.
     
     ifun
       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.
     
     the_rest
       Everything else on the line.
     """
     def __init__(self, line, continue_prompt):
         self.line            = line
         self.continue_prompt = continue_prompt
         self.pre, self.ifun, self.the_rest = split_user_input(line)
 
         self.pre_char       = self.pre.strip()
         if self.pre_char:
             self.pre_whitespace = '' # No whitespace allowd before esc chars
         else: 
             self.pre_whitespace = self.pre
 
         self._oinfo = None
 
     def ofind(self, ip):
         """Do a full, attribute-walking lookup of the ifun in the various
         namespaces for the given IPython InteractiveShell instance.
 
         Return a dict with keys: found,obj,ospace,ismagic
 
         Note: can cause state changes because of calling getattr, but should
         only be run if autocall is on and if the line hasn't matched any
         other, less dangerous handlers.
 
         Does cache the results of the call, so can be called multiple times
         without worrying about *further* damaging state.
         """
         if not self._oinfo:
             self._oinfo = ip._ofind(self.ifun)
         return self._oinfo
 
     def __str__(self):                                                         
         return "Lineinfo [%s|%s|%s]" %(self.pre,self.ifun,self.the_rest) 
 
 
 #-----------------------------------------------------------------------------
 # Main Prefilter manager
 #-----------------------------------------------------------------------------
 
 
 class PrefilterManager(Component):
     """Main prefilter component.
 
     The IPython prefilter is run on all user input before it is run.  The
     prefilter consumes lines of input and produces transformed lines of 
-    input.  The implementation consists of checkers and handlers.  The 
-    checkers inspect the input line and select which handler will be used
-    to transform the input line.
+    input.
+
+    The iplementation consists of two phases:
+
+    1. Transformers
+    2. Checkers and handlers
+
+    Over time, we plan on deprecating the checkers and handlers and doing
+    everything in the transformers.
+
+    The transformers are instances of :class:`PrefilterTransformer` and have
+    a single method :meth:`transform` that takes a line and returns a
+    transformed line.  The transformation can be accomplished using any
+    tool, but our current ones use regular expressions for speed.  We also
+    ship :mod:`pyparsing` in :mod:`IPython.external` for use in transformers.
+
+    After all the transformers have been run, the line is fed to the checkers,
+    which are instances of :class:`PrefilterChecker`.  The line is passed to
+    the :meth:`check` method, which either returns `None` or a 
+    :class:`PrefilterHandler` instance.  If `None` is returned, the other
+    checkers are tried.  If an :class:`PrefilterHandler` instance is returned,
+    the line is passed to the :meth:`handle` method of the returned
+    handler and no further checkers are tried.
+    
+    Both transformers and checkers have a `priority` attribute, that determines
+    the order in which they are called.  Smaller priorities are tried first.
+
+    Both transformers and checkers also have `enabled` attribute, which is
+    a boolean that determines if the instance is used.
+
+    Users or developers can change the priority or enabled attribute of
+    transformers or checkers, but they must call the :meth:`sort_checkers`
+    or :meth`sort_transformers` method after changing the priority.
     """
 
     multi_line_specials = CBool(True, config=True)
 
     def __init__(self, parent, config=None):
         super(PrefilterManager, self).__init__(parent, config=config)
+        self.init_transformers()
         self.init_handlers()
         self.init_checkers()
 
     @auto_attr
     def shell(self):
         return Component.get_instances(
             root=self.root,
             klass='IPython.core.iplib.InteractiveShell')[0]
 
+    #-------------------------------------------------------------------------
+    # API for managing transformers
+    #-------------------------------------------------------------------------
+
+    def init_transformers(self):
+        """Create the default transformers."""
+        self._transformers = []
+        for transformer_cls in _default_transformers:
+            transformer_cls(self, config=self.config)
+
+    def sort_transformers(self):
+        """Sort the transformers by priority.
+
+        This must be called after the priority of a transformer is changed.
+        The :meth:`register_transformer` method calls this automatically.
+        """
+        self._transformers.sort(cmp=lambda x,y: x.priority-y.priority)
+
+    @property
+    def transformers(self):
+        """Return a list of checkers, sorted by priority."""
+        return self._transformers
+
+    def register_transformer(self, transformer):
+        """Register a transformer instance."""
+        if transformer not in self._transformers:
+            self._transformers.append(transformer)
+            self.sort_transformers()
+
+    def unregister_transformer(self, transformer):
+        """Unregister a transformer instance."""
+        if transformer in self._transformers:
+            self._transformers.remove(transformer)
+
+    #-------------------------------------------------------------------------
+    # API for managing checkers
+    #-------------------------------------------------------------------------
+
     def init_checkers(self):
+        """Create the default checkers."""
         self._checkers = []
         for checker in _default_checkers:
-            self._checkers.append(checker(self, config=self.config))
+            checker(self, config=self.config)
+
+    def sort_checkers(self):
+        """Sort the checkers by priority.
+
+        This must be called after the priority of a checker is changed.
+        The :meth:`register_checker` method calls this automatically.
+        """
+        self._checkers.sort(cmp=lambda x,y: x.priority-y.priority)
+
+    @property
+    def checkers(self):
+        """Return a list of checkers, sorted by priority."""
+        return self._checkers
+
+    def register_checker(self, checker):
+        """Register a checker instance."""
+        if checker not in self._checkers:
+            self._checkers.append(checker)
+            self.sort_checkers()
+
+    def unregister_checker(self, checker):
+        """Unregister a checker instance."""
+        if checker in self._checkers:
+            self._checkers.remove(checker)
+
+    #-------------------------------------------------------------------------
+    # API for managing checkers
+    #-------------------------------------------------------------------------
 
     def init_handlers(self):
+        """Create the default handlers."""
         self._handlers = {}
         self._esc_handlers = {}
         for handler in _default_handlers:
             handler(self, config=self.config)
 
     @property
-    def sorted_checkers(self):
-        """Return a list of checkers, sorted by priority."""
-        return sorted(self._checkers, cmp=lambda x,y: x.priority-y.priority)
+    def handlers(self):
+        """Return a dict of all the handlers."""
+        return self._handlers
 
     def register_handler(self, name, handler, esc_strings):
         """Register a handler instance by name with esc_strings."""
         self._handlers[name] = handler
         for esc_str in esc_strings:
             self._esc_handlers[esc_str] = handler
 
     def unregister_handler(self, name, handler, esc_strings):
         """Unregister a handler instance by name with esc_strings."""
         try:
             del self._handlers[name]
         except KeyError:
             pass
         for esc_str in esc_strings:
             h = self._esc_handlers.get(esc_str)
             if h is handler:
                 del self._esc_handlers[esc_str]
 
     def get_handler_by_name(self, name):
         """Get a handler by its name."""
         return self._handlers.get(name)
 
     def get_handler_by_esc(self, esc_str):
         """Get a handler by its escape string."""
         return self._esc_handlers.get(esc_str)
 
+    #-------------------------------------------------------------------------
+    # Main prefiltering API
+    #-------------------------------------------------------------------------
+
     def prefilter_line_info(self, line_info):
-        """Prefilter a line that has been converted to a LineInfo object."""
+        """Prefilter a line that has been converted to a LineInfo object.
+
+        This implements the checker/handler part of the prefilter pipe.
+        """
         # print "prefilter_line_info: ", line_info
         handler = self.find_handler(line_info)
         return handler.handle(line_info)
 
     def find_handler(self, line_info):
         """Find a handler for the line_info by trying checkers."""
-        for checker in self.sorted_checkers:
-            handler = checker.check(line_info)
-            if handler:
-                # print "Used checker: ", checker
-                # print "Using handler: ", handler
-                return handler
+        for checker in self.checkers:
+            if checker.enabled:
+                handler = checker.check(line_info)
+                if handler:
+                    return handler
         return self.get_handler_by_name('normal')
 
+    def transform_line(self, line, continue_prompt):
+        """Calls the enabled transformers in order of increasing priority."""
+        for transformer in self.transformers:
+            if transformer.enabled:
+                line = transformer.transform(line, continue_prompt)
+        return line
+
     def prefilter_line(self, line, continue_prompt):
-        """Prefilter a single input line as text."""
+        """Prefilter a single input line as text.
+
+        This method prefilters a single line of text by calling the
+        transformers and then the checkers/handlers.
+        """
 
         # print "prefilter_line: ", line, continue_prompt
         # All handlers *must* return a value, even if it's blank ('').
 
         # Lines are NOT logged here. Handlers should process the line as
         # needed, update the cache AND log it (so that the input cache array
         # stays synced).
 
-        # growl.notify("_prefilter: ", "line = %s\ncontinue_prompt = %s" % (line, continue_prompt))
-
         # save the line away in case we crash, so the post-mortem handler can
         # record it
         self.shell._last_input_line = line
 
         if not line:
             # Return immediately on purely empty lines, so that if the user
             # previously typed some whitespace that started a continuation
             # prompt, he can break out of that loop with just an empty line.
             # This is how the default python prompt works.
 
             # Only return if the accumulated input buffer was just whitespace!
             if ''.join(self.shell.buffer).isspace():
                 self.shell.buffer[:] = []
             return ''
-        
+
+        # At this point, we invoke our transformers.
+        if not continue_prompt or (continue_prompt and self.multi_line_specials):
+            line = self.transform_line(line, continue_prompt)
+
+        # Now we compute line_info for the checkers and handlers
         line_info = LineInfo(line, continue_prompt)
         
         # the input history needs to track even empty lines
         stripped = line.strip()
 
-        normal_handler = self.get_handler_by_name('normal')        
+        normal_handler = self.get_handler_by_name('normal')
         if not stripped:
             if not continue_prompt:
                 self.shell.outputcache.prompt_count -= 1
 
             return normal_handler.handle(line_info)
 
         # special handlers are only allowed for single line statements
         if continue_prompt and not self.multi_line_specials:
             return normal_handler.handle(line_info)
 
         prefiltered = self.prefilter_line_info(line_info)
         # print "prefiltered line: %r" % prefiltered
         return prefiltered
 
     def prefilter_lines(self, lines, continue_prompt):
         """Prefilter multiple input lines of text.
 
-        Covers cases where there are multiple lines in the user entry,
+        This is the main entry point for prefiltering multiple lines of
+        input.  This simply calls :meth:`prefilter_line` for each line of
+        input.
+
+        This covers cases where there are multiple lines in the user entry,
         which is the case when the user goes back to a multiline history
         entry and presses enter.
         """
-        # growl.notify("multiline_prefilter: ", "%s\n%s" % (line, continue_prompt))
         out = []
         for line in lines.rstrip('\n').split('\n'):
             out.append(self.prefilter_line(line, continue_prompt))
-        # growl.notify("multiline_prefilter return: ", '\n'.join(out))
         return '\n'.join(out)
 
 
 #-----------------------------------------------------------------------------
+# Prefilter transformers
+#-----------------------------------------------------------------------------
+
+
+class PrefilterTransformer(Component):
+    """Transform a line of user input."""
+
+    priority = Int(100, config=True)
+    shell = Any
+    prefilter_manager = Any
+    enabled = Bool(True, config=True)
+
+    def __init__(self, parent, config=None):
+        super(PrefilterTransformer, self).__init__(parent, config=config)
+        self.prefilter_manager.register_transformer(self)
+
+    @auto_attr
+    def shell(self):
+        return Component.get_instances(
+            root=self.root,
+            klass='IPython.core.iplib.InteractiveShell')[0]
+
+    @auto_attr
+    def prefilter_manager(self):
+        return PrefilterManager.get_instances(root=self.root)[0]
+
+    def transform(self, line, continue_prompt):
+        """Transform a line, returning the new one."""
+        return None
+
+    def __repr__(self):
+        return "<%s(priority=%r, enabled=%r)>" % (
+            self.__class__.__name__, self.priority, self.enabled)
+
+
+_assign_system_re = re.compile(r'(?P<lhs>(\s*)([\w\.]+)((\s*,\s*[\w\.]+)*))'
+                               r'\s*=\s*!(?P<cmd>.*)')
+
+
+class AssignSystemTransformer(PrefilterTransformer):
+    """Handle the `files = !ls` syntax."""
+
+    priority = Int(100, config=True)
+
+    def transform(self, line, continue_prompt):
+        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*%(?P<cmd>.*)')
+
+class AssignMagicTransformer(PrefilterTransformer):
+    """Handle the `a = %who` syntax."""
+
+    priority = Int(200, config=True)
+
+    def transform(self, line, continue_prompt):
+        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
+
+
+#-----------------------------------------------------------------------------
 # Prefilter checkers
 #-----------------------------------------------------------------------------
 
 
 class PrefilterChecker(Component):
     """Inspect an input line and return a handler for that line."""
 
     priority = Int(100, config=True)
     shell = Any
     prefilter_manager = Any
+    enabled = Bool(True, config=True)
 
     def __init__(self, parent, config=None):
         super(PrefilterChecker, self).__init__(parent, config=config)
+        self.prefilter_manager.register_checker(self)
 
     @auto_attr
     def shell(self):
         return Component.get_instances(
             root=self.root,
             klass='IPython.core.iplib.InteractiveShell')[0]
 
     @auto_attr
     def prefilter_manager(self):
         return PrefilterManager.get_instances(root=self.root)[0]
 
     def check(self, line_info):
-        """Inspect line_info and return a handler or None."""
+        """Inspect line_info and return a handler instance or None."""
         return None
 
-    def __str__(self):
-        return "<%s(priority=%i)>" % (self.__class__.__name__, self.priority)
+    def __repr__(self):
+        return "<%s(priority=%r, enabled=%r)>" % (
+            self.__class__.__name__, self.priority, self.enabled)
+
 
 class EmacsChecker(PrefilterChecker):
 
     priority = Int(100, config=True)
+    enabled = Bool(False, config=True)
 
     def check(self, line_info):
         "Emacs ipython-mode tags certain input lines."
         if line_info.line.endswith('# PYTHON-MODE'):
             return self.prefilter_manager.get_handler_by_name('emacs')
         else:
             return None
 
 
 class ShellEscapeChecker(PrefilterChecker):
 
     priority = Int(200, config=True)
 
     def check(self, line_info):
         if line_info.line.lstrip().startswith(ESC_SHELL):
             return self.prefilter_manager.get_handler_by_name('shell')
 
 
 class IPyAutocallChecker(PrefilterChecker):
 
     priority = Int(300, config=True)
 
     def check(self, line_info):
         "Instances of IPyAutocall in user_ns get autocalled immediately"
         obj = self.shell.user_ns.get(line_info.ifun, None)
         if isinstance(obj, IPyAutocall):
             obj.set_ip(self.shell)
             return self.prefilter_manager.get_handler_by_name('auto')
         else:
             return None
 
 
 class MultiLineMagicChecker(PrefilterChecker):
 
     priority = Int(400, config=True)
 
     def check(self, line_info):
         "Allow ! and !! in multi-line statements if multi_line_specials is on"
         # Note that this one of the only places we check the first character of
         # ifun and *not* the pre_char.  Also note that the below test matches
         # both ! and !!.    
         if line_info.continue_prompt \
             and self.prefilter_manager.multi_line_specials:
                 if line_info.ifun.startswith(ESC_MAGIC):
                     return self.prefilter_manager.get_handler_by_name('magic')
         else:
             return None
 
 
 class EscCharsChecker(PrefilterChecker):
 
     priority = Int(500, config=True)
 
     def check(self, line_info):
         """Check for escape character and return either a handler to handle it,
         or None if there is no escape char."""
         if line_info.line[-1] == ESC_HELP \
                and line_info.pre_char != ESC_SHELL \
                and line_info.pre_char != ESC_SH_CAP:
             # the ? can be at the end, but *not* for either kind of shell escape,
             # because a ? can be a vaild final char in a shell cmd
             return self.prefilter_manager.get_handler_by_name('help')
         else:
             # This returns None like it should if no handler exists
             return self.prefilter_manager.get_handler_by_esc(line_info.pre_char)
 
 
-_assign_system_re = re.compile('\s*=\s*!(?P<cmd>.*)')
-_assign_magic_re = re.compile('\s*=\s*%(?P<cmd>.*)')
-
-
 class AssignmentChecker(PrefilterChecker):
 
     priority = Int(600, config=True)
 
     def check(self, line_info):
         """Check to see if user is assigning to a var for the first time, in
         which case we want to avoid any sort of automagic / autocall games.
     
         This allows users to assign to either alias or magic names true python
         variables (the magic/alias systems always take second seat to true
         python code).  E.g. ls='hi', or ls,that=1,2"""
         if line_info.the_rest:
             if line_info.the_rest[0] in '=,':
-                # m = _assign_system_re.match(line_info.the_rest)
-                # if m is not None:
-                #     return self.prefilter_manager.get_handler_by_name('assign_system')
-                # m = _assign_magic_re.match(line_info.the_rest)
-                # if m is not None:
-                #     return self.prefilter_manager.get_handler_by_name('assign_magic')
                 return self.prefilter_manager.get_handler_by_name('normal')
         else:
             return None
 
 
 class AutoMagicChecker(PrefilterChecker):
 
     priority = Int(700, config=True)
 
     def check(self, line_info):
         """If the ifun is magic, and automagic is on, run it.  Note: normal,
         non-auto magic would already have been triggered via '%' in
         check_esc_chars. This just checks for automagic.  Also, before
         triggering the magic handler, make sure that there is nothing in the
         user namespace which could shadow it."""
         if not self.shell.automagic or not hasattr(self.shell,'magic_'+line_info.ifun):
             return None
 
         # We have a likely magic method.  Make sure we should actually call it.
         if line_info.continue_prompt and not self.shell.multi_line_specials:
             return None
 
         head = line_info.ifun.split('.',1)[0]
         if is_shadowed(head, self.shell):
             return None
 
         return self.prefilter_manager.get_handler_by_name('magic')
 
 
 class AliasChecker(PrefilterChecker):
 
     priority = Int(800, config=True)
 
     @auto_attr
     def alias_manager(self):
         return AliasManager.get_instances(root=self.root)[0]
 
     def check(self, line_info):
         "Check if the initital identifier on the line is an alias."
         # Note: aliases can not contain '.'
         head = line_info.ifun.split('.',1)[0]
         if line_info.ifun not in self.alias_manager \
                or head not in self.alias_manager \
                or is_shadowed(head, self.shell):
             return None
 
         return self.prefilter_manager.get_handler_by_name('alias')
 
 
 class PythonOpsChecker(PrefilterChecker):
 
     priority = Int(900, config=True)
 
     def check(self, line_info):
         """If the 'rest' of the line begins with a function call or pretty much
         any python operator, we should simply execute the line (regardless of
         whether or not there's a possible autocall expansion).  This avoids
         spurious (and very confusing) geattr() accesses."""
         if line_info.the_rest and line_info.the_rest[0] in '!=()<>,+*/%^&|':
             return self.prefilter_manager.get_handler_by_name('normal')
         else:
             return None
 
 
 class AutocallChecker(PrefilterChecker):
 
     priority = Int(1000, config=True)
 
     def check(self, line_info):
         "Check if the initial word/function is callable and autocall is on."
         if not self.shell.autocall:
             return None
 
         oinfo = line_info.ofind(self.shell) # This can mutate state via getattr
         if not oinfo['found']:
             return None
         
         if callable(oinfo['obj']) \
                and (not re_exclude_auto.match(line_info.the_rest)) \
                and re_fun_name.match(line_info.ifun):
             return self.prefilter_manager.get_handler_by_name('auto')
         else:
             return None
 
 
 #-----------------------------------------------------------------------------
 # Prefilter handlers
 #-----------------------------------------------------------------------------
 
 
 class PrefilterHandler(Component):
 
     handler_name = Str('normal')
     esc_strings = List([])
     shell = Any
     prefilter_manager = Any
 
     def __init__(self, parent, config=None):
         super(PrefilterHandler, self).__init__(parent, config=config)
         self.prefilter_manager.register_handler(
             self.handler_name,
             self,
             self.esc_strings
         )
 
     @auto_attr
     def shell(self):
         return Component.get_instances(
             root=self.root,
             klass='IPython.core.iplib.InteractiveShell')[0]
 
     @auto_attr
     def prefilter_manager(self):
         return PrefilterManager.get_instances(root=self.root)[0]
 
     def handle(self, line_info):
         # print "normal: ", line_info
         """Handle normal input lines. Use as a template for handlers."""
 
         # With autoindent on, we need some way to exit the input loop, and I
         # don't want to force the user to have to backspace all the way to
         # clear the line.  The rule will be in this case, that either two
         # lines of pure whitespace in a row, or a line of pure whitespace but
         # of a size different to the indent level, will exit the input loop.
         line = line_info.line
         continue_prompt = line_info.continue_prompt
 
         if (continue_prompt and self.shell.autoindent and line.isspace() and
             (0 < abs(len(line) - self.shell.indent_current_nsp) <= 2 or
              (self.shell.buffer[-1]).isspace() )):
             line = ''
 
         self.shell.log(line, line, continue_prompt)
         return line
 
     def __str__(self):
         return "<%s(name=%s)>" % (self.__class__.__name__, self.handler_name)
 
-class AssignSystemHandler(PrefilterHandler):
-
-    handler_name = Str('assign_system')
-
-    @auto_attr
-    def normal_handler(self):
-        return self.prefilter_manager.get_handler_by_name('normal')
-
-    def handle(self, line_info):
-        new_line = line_info.line
-        m = _assign_system_re.match(line_info.the_rest)
-        if m is not None:
-            cmd = m.group('cmd')
-            expr = make_quoted_expr("sc -l =%s" % cmd)
-            new_line = '%s%s = get_ipython().magic(%s)' % (line_info.pre_whitespace,
-                line_info.ifun, expr)
-        self.shell.log(line_info.line, new_line, line_info.continue_prompt)
-        return new_line
-
-
-class AssignMagicHandler(PrefilterHandler):
-
-    handler_name = Str('assign_magic')
-
-    @auto_attr
-    def normal_handler(self):
-        return self.prefilter_manager.get_handler_by_name('normal')
-
-    def handle(self, line_info):
-        new_line = line_info.line
-        m = _assign_magic_re.match(line_info.the_rest)
-        if m is not None:
-            cmd = m.group('cmd')
-            expr = make_quoted_expr(cmd)
-            new_line = '%s%s = get_ipython().magic(%s)' % (line_info.pre_whitespace,
-                line_info.ifun, expr)
-        self.shell.log(line_info.line, new_line, line_info.continue_prompt)
-        return new_line
-
 
 class AliasHandler(PrefilterHandler):
 
     handler_name = Str('alias')
 
     @auto_attr
     def alias_manager(self):
         return AliasManager.get_instances(root=self.root)[0]
 
     def handle(self, line_info):
         """Handle alias input lines. """
         transformed = self.alias_manager.expand_aliases(line_info.ifun,line_info.the_rest)
         # pre is needed, because it carries the leading whitespace.  Otherwise
         # aliases won't work in indented sections.
         line_out = '%sget_ipython().system(%s)' % (line_info.pre_whitespace,
                                          make_quoted_expr(transformed))
         
         self.shell.log(line_info.line, line_out, line_info.continue_prompt)
         return line_out
 
 
 class ShellEscapeHandler(PrefilterHandler):
 
     handler_name = Str('shell')
     esc_strings = List([ESC_SHELL, ESC_SH_CAP])
 
     def handle(self, line_info):
         """Execute the line in a shell, empty return value"""
         magic_handler = self.prefilter_manager.get_handler_by_name('magic')
 
         line = line_info.line
         if line.lstrip().startswith(ESC_SH_CAP):
             # rewrite LineInfo's line, ifun and the_rest to properly hold the
             # call to %sx and the actual command to be executed, so
             # handle_magic can work correctly.  Note that this works even if
             # the line is indented, so it handles multi_line_specials
             # properly.
             new_rest = line.lstrip()[2:]
             line_info.line = '%ssx %s' % (ESC_MAGIC, new_rest)
             line_info.ifun = 'sx'
             line_info.the_rest = new_rest
             return magic_handler.handle(line_info)
         else:
             cmd = line.lstrip().lstrip(ESC_SHELL)
             line_out = '%sget_ipython().system(%s)' % (line_info.pre_whitespace,
                                              make_quoted_expr(cmd))
         # update cache/log and return
         self.shell.log(line, line_out, line_info.continue_prompt)
         return line_out
 
 
 class MagicHandler(PrefilterHandler):
 
     handler_name = Str('magic')
     esc_strings = List([ESC_MAGIC])
 
     def handle(self, line_info):
         """Execute magic functions."""
         ifun    = line_info.ifun
         the_rest = line_info.the_rest
         cmd = '%sget_ipython().magic(%s)' % (line_info.pre_whitespace,
                                    make_quoted_expr(ifun + " " + the_rest))
         self.shell.log(line_info.line, cmd, line_info.continue_prompt)
         return cmd
 
 
 class AutoHandler(PrefilterHandler):
 
     handler_name = Str('auto')
     esc_strings = List([ESC_PAREN, ESC_QUOTE, ESC_QUOTE2])
 
     def handle(self, line_info):
         """Hande lines which can be auto-executed, quoting if requested."""
         line    = line_info.line
         ifun    = line_info.ifun
         the_rest = line_info.the_rest
         pre     = line_info.pre
         continue_prompt = line_info.continue_prompt
         obj = line_info.ofind(self)['obj']
 
         #print 'pre <%s> ifun <%s> rest <%s>' % (pre,ifun,the_rest)  # dbg
 
         # This should only be active for single-line input!
         if continue_prompt:
             self.log(line,line,continue_prompt)
             return line
 
         force_auto = isinstance(obj, IPyAutocall)
         auto_rewrite = True
         
         if pre == ESC_QUOTE:
             # Auto-quote splitting on whitespace
             newcmd = '%s("%s")' % (ifun,'", "'.join(the_rest.split()) )
         elif pre == ESC_QUOTE2:
             # Auto-quote whole string
             newcmd = '%s("%s")' % (ifun,the_rest)
         elif pre == ESC_PAREN:
             newcmd = '%s(%s)' % (ifun,",".join(the_rest.split()))
         else:
             # Auto-paren.
             # We only apply it to argument-less calls if the autocall
             # parameter is set to 2.  We only need to check that autocall is <
             # 2, since this function isn't called unless it's at least 1.
             if not the_rest and (self.shell.autocall < 2) and not force_auto:
                 newcmd = '%s %s' % (ifun,the_rest)
                 auto_rewrite = False
             else:
                 if not force_auto and the_rest.startswith('['):
                     if hasattr(obj,'__getitem__'):
                         # Don't autocall in this case: item access for an object
                         # which is BOTH callable and implements __getitem__.
                         newcmd = '%s %s' % (ifun,the_rest)
                         auto_rewrite = False
                     else:
                         # if the object doesn't support [] access, go ahead and
                         # autocall
                         newcmd = '%s(%s)' % (ifun.rstrip(),the_rest)
                 elif the_rest.endswith(';'):
                     newcmd = '%s(%s);' % (ifun.rstrip(),the_rest[:-1])
                 else:
                     newcmd = '%s(%s)' % (ifun.rstrip(), the_rest)
 
         if auto_rewrite:
             rw = self.shell.outputcache.prompt1.auto_rewrite() + newcmd
             
             try:
                 # plain ascii works better w/ pyreadline, on some machines, so
                 # we use it and only print uncolored rewrite if we have unicode
                 rw = str(rw)
                 print >>Term.cout, rw
             except UnicodeEncodeError:
                 print "-------------->" + newcmd
             
         # log what is now valid Python, not the actual user input (without the
         # final newline)
         self.shell.log(line,newcmd,continue_prompt)
         return newcmd
 
 
 class HelpHandler(PrefilterHandler):
 
     handler_name = Str('help')
     esc_strings = List([ESC_HELP])
 
     def handle(self, line_info):
         """Try to get some help for the object.
 
         obj? or ?obj   -> basic information.
         obj?? or ??obj -> more details.
         """
         normal_handler = self.prefilter_manager.get_handler_by_name('normal')
         line = line_info.line
         # We need to make sure that we don't process lines which would be
         # otherwise valid python, such as "x=1 # what?"
         try:
             codeop.compile_command(line)
         except SyntaxError:
             # We should only handle as help stuff which is NOT valid syntax
             if line[0]==ESC_HELP:
                 line = line[1:]
             elif line[-1]==ESC_HELP:
                 line = line[:-1]
             self.shell.log(line, '#?'+line, line_info.continue_prompt)
             if line:
                 #print 'line:<%r>' % line  # dbg
                 self.shell.magic_pinfo(line)
             else:
                 page(self.shell.usage, screen_lines=self.shell.usable_screen_length)
             return '' # Empty string is needed here!
         except:
             raise
             # Pass any other exceptions through to the normal handler
             return normal_handler.handle(line_info)
         else:
             raise
             # If the code compiles ok, we should handle it normally
             return normal_handler.handle(line_info)
 
 
 class EmacsHandler(PrefilterHandler):
 
     handler_name = Str('emacs')
     esc_strings = List([])
 
     def handle(self, line_info):
         """Handle input lines marked by python-mode."""
 
         # Currently, nothing is done.  Later more functionality can be added
         # here if needed.
 
         # The input cache shouldn't be updated
         return line_info.line
 
 
 #-----------------------------------------------------------------------------
 # Defaults
 #-----------------------------------------------------------------------------
 
 
+_default_transformers = [
+    AssignSystemTransformer,
+    AssignMagicTransformer
+]
+
 _default_checkers = [
     EmacsChecker,
     ShellEscapeChecker,
     IPyAutocallChecker,
     MultiLineMagicChecker,
     EscCharsChecker,
     AssignmentChecker,
     AutoMagicChecker,
     AliasChecker,
     PythonOpsChecker,
     AutocallChecker
 ]
 
 _default_handlers = [
     PrefilterHandler,
     AliasHandler,
     ShellEscapeHandler,
     MagicHandler,
     AutoHandler,
     HelpHandler,
     EmacsHandler
-    # AssignSystemHandler,
-    # AssignMagicHandler
 ]