Fix tab-completion crash when no results were returned.

IPython/core/completer.py

@@ -1,841 +1,842 b''
 """Word completion for IPython.
 
 This module is a fork of the rlcompleter module in the Python standard
 library.  The original enhancements made to rlcompleter have been sent
 upstream and were accepted as of Python 2.3, but we need a lot more
 functionality specific to IPython, so this module will continue to live as an
 IPython-specific utility.
 
 Original rlcompleter documentation:
 
 This requires the latest extension to the readline module (the
 completes keywords, built-ins and globals in __main__; when completing
 NAME.NAME..., it evaluates (!) the expression up to the last dot and
 completes its attributes.
 
 It's very cool to do "import string" type "string.", hit the
 completion key (twice), and see the list of names defined by the
 string module!
 
 Tip: to use the tab key as the completion key, call
 
     readline.parse_and_bind("tab: complete")
 
 Notes:
 
 - Exceptions raised by the completer function are *ignored* (and
 generally cause the completion to fail).  This is a feature -- since
 readline sets the tty device in raw (or cbreak) mode, printing a
 traceback wouldn't work well without some complicated hoopla to save,
 reset and restore the tty state.
 
 - The evaluation of the NAME.NAME... form may cause arbitrary
 application defined code to be executed if an object with a
 __getattr__ hook is found.  Since it is the responsibility of the
 application (or the user) to enable this feature, I consider this an
 acceptable risk.  More complicated expressions (e.g. function calls or
 indexing operations) are *not* evaluated.
 
 - GNU readline is also used by the built-in functions input() and
 raw_input(), and thus these also benefit/suffer from the completer
 features.  Clearly an interactive application can benefit by
 specifying its own completer function and using raw_input() for all
 its input.
 
 - When the original stdin is not a tty device, GNU readline is never
 used, and this module (and the readline module) are silently inactive.
 """
 
 #*****************************************************************************
 #
 # Since this file is essentially a minimally modified copy of the rlcompleter
 # module which is part of the standard Python distribution, I assume that the
 # proper procedure is to maintain its copyright as belonging to the Python
 # Software Foundation (in addition to my own, for all new code).
 #
 #       Copyright (C) 2008-2010 IPython Development Team
 #       Copyright (C) 2001-2007 Fernando Perez. <[e-mail]>
 #       Copyright (C) 2001 Python Software Foundation, www.python.org
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #
 #*****************************************************************************
 from __future__ import print_function
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import __builtin__
 import __main__
 import glob
 import inspect
 import itertools
 import keyword
 import os
 import re
 import shlex
 import sys
 
 from IPython.core.error import TryNext
 from IPython.core.prefilter import ESC_MAGIC
 from IPython.utils import generics
 from IPython.utils import io
 from IPython.utils.dir2 import dir2
 
 #-----------------------------------------------------------------------------
 # Globals
 #-----------------------------------------------------------------------------
 
 # Public API
 __all__ = ['Completer','IPCompleter']
 
 if sys.platform == 'win32':
     PROTECTABLES = ' '
 else:
     PROTECTABLES = ' ()'
 
 #-----------------------------------------------------------------------------
 # Main functions and classes
 #-----------------------------------------------------------------------------
 
 def protect_filename(s):
     """Escape a string to protect certain characters."""
     
     return "".join([(ch in PROTECTABLES and '\\' + ch or ch)
                     for ch in s])
 
 
 def mark_dirs(matches):
     """Mark directories in input list by appending '/' to their names."""
     out = []
     isdir = os.path.isdir
     for x in matches:
         if isdir(x):
             out.append(x+'/')
         else:
             out.append(x)
     return out
 
 
 def expand_user(path):
     """Expand '~'-style usernames in strings.
 
     This is similar to :func:`os.path.expanduser`, but it computes and returns
     extra information that will be useful if the input was being used in
     computing completions, and you wish to return the completions with the
     original '~' instead of its expanded value.
 
     Parameters
     ----------
     path : str
       String to be expanded.  If no ~ is present, the output is the same as the
       input.
       
     Returns
     -------
     newpath : str
       Result of ~ expansion in the input path.
     tilde_expand : bool
       Whether any expansion was performed or not.
     tilde_val : str
       The value that ~ was replaced with.
     """
     # Default values
     tilde_expand = False
     tilde_val = ''
     newpath = path
     
     if path.startswith('~'):
         tilde_expand = True
         rest = path[1:]
         newpath = os.path.expanduser(path)
         tilde_val = newpath.replace(rest, '')
 
     return newpath, tilde_expand, tilde_val
 
 
 def compress_user(path, tilde_expand, tilde_val):
     """Does the opposite of expand_user, with its outputs.
     """
     if tilde_expand:
         return path.replace(tilde_val, '~')
     else:
         return path
 
 
 def single_dir_expand(matches):
     "Recursively expand match lists containing a single dir."
 
     if len(matches) == 1 and os.path.isdir(matches[0]):
         # Takes care of links to directories also.  Use '/'
         # explicitly, even under Windows, so that name completions
         # don't end up escaped.
         d = matches[0]
         if d[-1] in ['/','\\']:
             d = d[:-1]
 
         subdirs = os.listdir(d)
         if subdirs:
             matches = [ (d + '/' + p) for p in subdirs]
             return single_dir_expand(matches)
         else:
             return matches
     else:
         return matches
 
 
 class Bunch(object): pass
 
 
 class CompletionSplitter(object):
     """An object to split an input line in a manner similar to readline.
 
     By having our own implementation, we can expose readline-like completion in
     a uniform manner to all frontends.  This object only needs to be given the
     line of text to be split and the cursor position on said line, and it
     returns the 'word' to be completed on at the cursor after splitting the
     entire line.
 
     What characters are used as splitting delimiters can be controlled by
     setting the `delims` attribute (this is a property that internally
     automatically builds the necessary """
 
     # Private interface
     
     # A string of delimiter characters.  The default value makes sense for
     # IPython's most typical usage patterns.
     _delims = ' \t\n`!@#$^&*()=+[{]}\\|;:\'",<>?'
 
     # The expression (a normal string) to be compiled into a regular expression
     # for actual splitting.  We store it as an attribute mostly for ease of
     # debugging, since this type of code can be so tricky to debug.
     _delim_expr = None
 
     # The regular expression that does the actual splitting
     _delim_re = None
 
     def __init__(self, delims=None):
         delims = CompletionSplitter._delims if delims is None else delims
         self.set_delims(delims)
 
     def set_delims(self, delims):
         """Set the delimiters for line splitting."""
         expr = '[' + ''.join('\\'+ c for c in delims) + ']'
         self._delim_re = re.compile(expr)
         self._delims = delims
         self._delim_expr = expr
 
     def get_delims(self):
         """Return the string of delimiter characters."""
         return self._delims
 
     def split_line(self, line, cursor_pos=None):
         """Split a line of text with a cursor at the given position.
         """
         l = line if cursor_pos is None else line[:cursor_pos]
         return self._delim_re.split(l)[-1]
 
 
 class Completer(object):
     def __init__(self, namespace=None, global_namespace=None):
         """Create a new completer for the command line.
 
         Completer([namespace,global_namespace]) -> completer instance.
 
         If unspecified, the default namespace where completions are performed
         is __main__ (technically, __main__.__dict__). Namespaces should be
         given as dictionaries.
 
         An optional second namespace can be given.  This allows the completer
         to handle cases where both the local and global scopes need to be
         distinguished.
 
         Completer instances should be used as the completion mechanism of
         readline via the set_completer() call:
 
         readline.set_completer(Completer(my_namespace).complete)
         """
 
         # Don't bind to namespace quite yet, but flag whether the user wants a
         # specific namespace or to use __main__.__dict__. This will allow us
         # to bind to __main__.__dict__ at completion time, not now.
         if namespace is None:
             self.use_main_ns = 1
         else:
             self.use_main_ns = 0
             self.namespace = namespace
 
         # The global namespace, if given, can be bound directly
         if global_namespace is None:
             self.global_namespace = {}
         else:
             self.global_namespace = global_namespace
 
     def complete(self, text, state):
         """Return the next possible completion for 'text'.
 
         This is called successively with state == 0, 1, 2, ... until it
         returns None.  The completion should begin with 'text'.
 
         """
         if self.use_main_ns:
             self.namespace = __main__.__dict__
             
         if state == 0:
             if "." in text:
                 self.matches = self.attr_matches(text)
             else:
                 self.matches = self.global_matches(text)
         try:
             return self.matches[state]
         except IndexError:
             return None
 
     def global_matches(self, text):
         """Compute matches when text is a simple name.
 
         Return a list of all keywords, built-in functions and names currently
         defined in self.namespace or self.global_namespace that match.
 
         """
         #print 'Completer->global_matches, txt=%r' % text # dbg
         matches = []
         match_append = matches.append
         n = len(text)
         for lst in [keyword.kwlist,
                     __builtin__.__dict__.keys(),
                     self.namespace.keys(),
                     self.global_namespace.keys()]:
             for word in lst:
                 if word[:n] == text and word != "__builtins__":
                     match_append(word)
         return matches
 
     def attr_matches(self, text):
         """Compute matches when text contains a dot.
 
         Assuming the text is of the form NAME.NAME....[NAME], and is
         evaluatable in self.namespace or self.global_namespace, it will be
         evaluated and its attributes (as revealed by dir()) are used as
         possible completions.  (For class instances, class members are are
         also considered.)
 
         WARNING: this can still invoke arbitrary C code, if an object
         with a __getattr__ hook is evaluated.
 
         """
 
         #print 'Completer->attr_matches, txt=%r' % text # dbg
         # Another option, seems to work great. Catches things like ''.<tab>
         m = re.match(r"(\S+(\.\w+)*)\.(\w*)$", text)
 
         if not m:
             return []
         
         expr, attr = m.group(1, 3)
         try:
             obj = eval(expr, self.namespace)
         except:
             try:
                 obj = eval(expr, self.global_namespace)
             except:
                 return []
 
         words = dir2(obj)
         
         try:
             words = generics.complete_object(obj, words)
         except TryNext:
             pass
         # Build match list to return
         n = len(attr)
         res = ["%s.%s" % (expr, w) for w in words if w[:n] == attr ]
         return res
 
 
 class IPCompleter(Completer):
     """Extension of the completer class with IPython-specific features"""
 
     def __init__(self, shell, namespace=None, global_namespace=None,
                  omit__names=0, alias_table=None, use_readline=True):
         """IPCompleter() -> completer
 
         Return a completer object suitable for use by the readline library
         via readline.set_completer().
 
         Inputs:
 
         - shell: a pointer to the ipython shell itself.  This is needed
         because this completer knows about magic functions, and those can
         only be accessed via the ipython instance.
 
         - namespace: an optional dict where completions are performed.
 
         - global_namespace: secondary optional dict for completions, to
         handle cases (such as IPython embedded inside functions) where
         both Python scopes are visible.
 
         - The optional omit__names parameter sets the completer to omit the
         'magic' names (__magicname__) for python objects unless the text
         to be completed explicitly starts with one or more underscores.
 
         - If alias_table is supplied, it should be a dictionary of aliases
         to complete.
 
         use_readline : bool, optional
           If true, use the readline library.  This completer can still function
           without readline, though in that case callers must provide some extra
           information on each call about the current line."""
 
         Completer.__init__(self, namespace, global_namespace)
 
         self.magic_escape = ESC_MAGIC
         self.splitter = CompletionSplitter()
 
         # Readline configuration, only used by the rlcompleter method.
         if use_readline:
             # We store the right version of readline so that later code 
             import IPython.utils.rlineimpl as readline
             self.readline = readline
         else:
             self.readline = None
 
         # List where completion matches will be stored
         self.matches = []
         self.omit__names = omit__names
         self.merge_completions = shell.readline_merge_completions
         self.shell = shell.shell
         if alias_table is None:
             alias_table = {}
         self.alias_table = alias_table
         # Regexp to split filenames with spaces in them
         self.space_name_re = re.compile(r'([^\\] )')
         # Hold a local ref. to glob.glob for speed
         self.glob = glob.glob
 
         # Determine if we are running on 'dumb' terminals, like (X)Emacs
         # buffers, to avoid completion problems.
         term = os.environ.get('TERM','xterm')
         self.dumb_terminal = term in ['dumb','emacs']
         
         # Special handling of backslashes needed in win32 platforms
         if sys.platform == "win32":
             self.clean_glob = self._clean_glob_win32
         else:
             self.clean_glob = self._clean_glob
 
         # All active matcher routines for completion
         self.matchers = [self.python_matches,
                          self.file_matches,
                          self.magic_matches,
                          self.alias_matches,
                          self.python_func_kw_matches,
                          ]
     
     # Code contributed by Alex Schmolck, for ipython/emacs integration
     def all_completions(self, text):
         """Return all possible completions for the benefit of emacs."""
 
         completions = []
         comp_append = completions.append
         try:
             for i in xrange(sys.maxint):
                 res = self.complete(text, i, text)
                 if not res:
                     break
                 comp_append(res)
         #XXX workaround for ``notDefined.<tab>``
         except NameError:
             pass
         return completions
     # /end Alex Schmolck code.
 
     def _clean_glob(self,text):
         return self.glob("%s*" % text)
 
     def _clean_glob_win32(self,text):
         return [f.replace("\\","/")
                 for f in self.glob("%s*" % text)]            
 
     def file_matches(self, text):
         """Match filenames, expanding ~USER type strings.
 
         Most of the seemingly convoluted logic in this completer is an
         attempt to handle filenames with spaces in them.  And yet it's not
         quite perfect, because Python's readline doesn't expose all of the
         GNU readline details needed for this to be done correctly.
 
         For a filename with a space in it, the printed completions will be
         only the parts after what's already been typed (instead of the
         full completions, as is normally done).  I don't think with the
         current (as of Python 2.3) Python readline it's possible to do
         better."""
 
         #io.rprint('Completer->file_matches: <%s>' % text) # dbg
 
         # chars that require escaping with backslash - i.e. chars
         # that readline treats incorrectly as delimiters, but we
         # don't want to treat as delimiters in filename matching
         # when escaped with backslash
         if text.startswith('!'):
             text = text[1:]
             text_prefix = '!'
         else:
             text_prefix = ''
             
         text_until_cursor = self.text_until_cursor
         open_quotes = 0  # track strings with open quotes
         try:
             lsplit = shlex.split(text_until_cursor)[-1]
         except ValueError:
             # typically an unmatched ", or backslash without escaped char.
             if text_until_cursor.count('"')==1:
                 open_quotes = 1
                 lsplit = text_until_cursor.split('"')[-1]
             elif text_until_cursor.count("'")==1:
                 open_quotes = 1
                 lsplit = text_until_cursor.split("'")[-1]
             else:
                 return []
         except IndexError:
             # tab pressed on empty line
             lsplit = ""
 
         if not open_quotes and lsplit != protect_filename(lsplit):
             # if protectables are found, do matching on the whole escaped
             # name
             has_protectables = 1
             text0,text = text,lsplit
         else:
             has_protectables = 0
             text = os.path.expanduser(text)
 
         if text == "":
             return [text_prefix + protect_filename(f) for f in self.glob("*")]
 
         m0 = self.clean_glob(text.replace('\\',''))
         if has_protectables:
             # If we had protectables, we need to revert our changes to the
             # beginning of filename so that we don't double-write the part
             # of the filename we have so far
             len_lsplit = len(lsplit)
             matches = [text_prefix + text0 + 
                        protect_filename(f[len_lsplit:]) for f in m0]
         else:
             if open_quotes:
                 # if we have a string with an open quote, we don't need to
                 # protect the names at all (and we _shouldn't_, as it
                 # would cause bugs when the filesystem call is made).
                 matches = m0
             else:
                 matches = [text_prefix + 
                            protect_filename(f) for f in m0]
 
         #io.rprint('mm', matches)  # dbg
         return mark_dirs(matches)
 
     def magic_matches(self, text):
         """Match magics"""
         #print 'Completer->magic_matches:',text,'lb',self.text_until_cursor # dbg
         # Get all shell magics now rather than statically, so magics loaded at
         # runtime show up too
         magics = self.shell.lsmagic()
         pre = self.magic_escape
         baretext = text.lstrip(pre)
         return [ pre+m for m in magics if m.startswith(baretext)]
 
     def alias_matches(self, text):
         """Match internal system aliases"""        
         #print 'Completer->alias_matches:',text,'lb',self.text_until_cursor # dbg
 
         # if we are not in the first 'item', alias matching
         # doesn't make sense - unless we are starting with 'sudo' command.
         main_text = self.text_until_cursor.lstrip()
         if ' ' in main_text and not main_text.startswith('sudo'):
             return []
         text = os.path.expanduser(text)
         aliases =  self.alias_table.keys()
         if text == '':
             return aliases
         else:
             return [a for a in aliases if a.startswith(text)]
 
     def python_matches(self,text):
         """Match attributes or global python names"""
 
         #print 'Completer->python_matches, txt=%r' % text # dbg
         if "." in text:
             try:
                 matches = self.attr_matches(text)
                 if text.endswith('.') and self.omit__names:
                     if self.omit__names == 1:
                         # true if txt is _not_ a __ name, false otherwise:
                         no__name = (lambda txt:
                                     re.match(r'.*\.__.*?__',txt) is None)
                     else:
                         # true if txt is _not_ a _ name, false otherwise:
                         no__name = (lambda txt:
                                     re.match(r'.*\._.*?',txt) is None)
                     matches = filter(no__name, matches)
             except NameError:
                 # catches <undefined attributes>.<tab>
                 matches = []
         else:
             matches = self.global_matches(text)
 
         return matches
 
     def _default_arguments(self, obj):
         """Return the list of default arguments of obj if it is callable,
         or empty list otherwise."""
 
         if not (inspect.isfunction(obj) or inspect.ismethod(obj)):
             # for classes, check for __init__,__new__
             if inspect.isclass(obj):
                 obj = (getattr(obj,'__init__',None) or
                        getattr(obj,'__new__',None))
             # for all others, check if they are __call__able
             elif hasattr(obj, '__call__'):
                 obj = obj.__call__
             # XXX: is there a way to handle the builtins ?
         try:
             args,_,_1,defaults = inspect.getargspec(obj)
             if defaults:
                 return args[-len(defaults):]
         except TypeError: pass
         return []
 
     def python_func_kw_matches(self,text):
         """Match named parameters (kwargs) of the last open function"""
 
         if "." in text: # a parameter cannot be dotted
             return []
         try: regexp = self.__funcParamsRegex
         except AttributeError:
             regexp = self.__funcParamsRegex = re.compile(r'''
                 '.*?' |    # single quoted strings or
                 ".*?" |    # double quoted strings or
                 \w+   |    # identifier
                 \S         # other characters
                 ''', re.VERBOSE | re.DOTALL)
         # 1. find the nearest identifier that comes before an unclosed
         # parenthesis e.g. for "foo (1+bar(x), pa", the candidate is "foo"
         tokens = regexp.findall(self.line_buffer)
         tokens.reverse()
         iterTokens = iter(tokens); openPar = 0
         for token in iterTokens:
             if token == ')':
                 openPar -= 1
             elif token == '(':
                 openPar += 1
                 if openPar > 0:
                     # found the last unclosed parenthesis
                     break
         else:
             return []
         # 2. Concatenate dotted names ("foo.bar" for "foo.bar(x, pa" )
         ids = []
         isId = re.compile(r'\w+$').match
         while True:
             try:
                 ids.append(iterTokens.next())
                 if not isId(ids[-1]):
                     ids.pop(); break
                 if not iterTokens.next() == '.':
                     break
             except StopIteration:
                 break
         # lookup the candidate callable matches either using global_matches
         # or attr_matches for dotted names
         if len(ids) == 1:
             callableMatches = self.global_matches(ids[0])
         else:
             callableMatches = self.attr_matches('.'.join(ids[::-1]))
         argMatches = []
         for callableMatch in callableMatches:
             try:
                 namedArgs = self._default_arguments(eval(callableMatch,
                                                          self.namespace))
             except:
                 continue
             for namedArg in namedArgs:
                 if namedArg.startswith(text):
                     argMatches.append("%s=" %namedArg)
         return argMatches
 
     def dispatch_custom_completer(self, text):
         #print "Custom! '%s' %s" % (text, self.custom_completers) # dbg
         line = self.line_buffer        
         if not line.strip():
             return None
         
         # Create a little structure to pass all the relevant information about
         # the current completion to any custom completer.
         event = Bunch()
         event.line = line
         event.symbol = text
         cmd = line.split(None,1)[0]
         event.command = cmd
         event.text_until_cursor = self.text_until_cursor
         
         #print "\ncustom:{%s]\n" % event # dbg
         
         # for foo etc, try also to find completer for %foo
         if not cmd.startswith(self.magic_escape):
             try_magic = self.custom_completers.s_matches(
                 self.magic_escape + cmd)            
         else:
             try_magic = []        
         
         for c in itertools.chain(self.custom_completers.s_matches(cmd),
                  try_magic,
                  self.custom_completers.flat_matches(self.text_until_cursor)):
             #print "try",c # dbg
             try:
                 res = c(event)
-                # first, try case sensitive match
-                withcase = [r for r in res if r.startswith(text)]
-                if withcase:
-                    return withcase
-                # if none, then case insensitive ones are ok too
-                text_low = text.lower()
-                return [r for r in res if r.lower().startswith(text_low)]
+                if res:
+                    # first, try case sensitive match
+                    withcase = [r for r in res if r.startswith(text)]
+                    if withcase:
+                        return withcase
+                    # if none, then case insensitive ones are ok too
+                    text_low = text.lower()
+                    return [r for r in res if r.lower().startswith(text_low)]
             except TryNext:
                 pass
             
         return None
                
     def complete(self, text=None, line_buffer=None, cursor_pos=None):
         """Return the state-th possible completion for 'text'.
 
         This is called successively with state == 0, 1, 2, ... until it
         returns None.  The completion should begin with 'text'.
 
         Note that both the text and the line_buffer are optional, but at least
         one of them must be given.
 
         Parameters
         ----------
           text : string, optional
             Text to perform the completion on.  If not given, the line buffer
             is split using the instance's CompletionSplitter object.
 
           line_buffer : string, optional
             If not given, the completer attempts to obtain the current line
             buffer via readline.  This keyword allows clients which are
             requesting for text completions in non-readline contexts to inform
             the completer of the entire text.
 
           cursor_pos : int, optional
             Index of the cursor in the full line buffer.  Should be provided by
             remote frontends where kernel has no access to frontend state.
         """
         #io.rprint('\nCOMP1 %r %r %r' % (text, line_buffer, cursor_pos))  # dbg
 
         # if the cursor position isn't given, the only sane assumption we can
         # make is that it's at the end of the line (the common case)
         if cursor_pos is None:
             cursor_pos = len(line_buffer) if text is None else len(text)
 
         # if text is either None or an empty string, rely on the line buffer
         if not text:
             text = self.splitter.split_line(line_buffer, cursor_pos)
 
         # If no line buffer is given, assume the input text is all there was
         if line_buffer is None:
             line_buffer = text
         
         self.line_buffer = line_buffer
         self.text_until_cursor = self.line_buffer[:cursor_pos]
         #io.rprint('\nCOMP2 %r %r %r' % (text, line_buffer, cursor_pos))  # dbg
 
         # Start with a clean slate of completions
         self.matches[:] = []
         custom_res = self.dispatch_custom_completer(text)
         if custom_res is not None:
             # did custom completers produce something?
             self.matches = custom_res
         else:
             # Extend the list of completions with the results of each
             # matcher, so we return results to the user from all
             # namespaces.
             if self.merge_completions:
                 self.matches = []
                 for matcher in self.matchers:
                     self.matches.extend(matcher(text))
             else:
                 for matcher in self.matchers:
                     self.matches = matcher(text)
                     if self.matches:
                         break
         # FIXME: we should extend our api to return a dict with completions for
         # different types of objects.  The rlcomplete() method could then
         # simply collapse the dict into a list for readline, but we'd have
         # richer completion semantics in other evironments.
         self.matches = sorted(set(self.matches))
         #io.rprint('COMP TEXT, MATCHES: %r, %r' % (text, self.matches)) # dbg
         return text, self.matches
 
     def rlcomplete(self, text, state):
         """Return the state-th possible completion for 'text'.
 
         This is called successively with state == 0, 1, 2, ... until it
         returns None.  The completion should begin with 'text'.
 
         Parameters
         ----------
           text : string
             Text to perform the completion on.
 
           state : int
             Counter used by readline.
         """
         if state==0:
 
             self.line_buffer = line_buffer = self.readline.get_line_buffer()
             cursor_pos = self.readline.get_endidx()
 
             #io.rprint("\nRLCOMPLETE: %r %r %r" %
             #          (text, line_buffer, cursor_pos) ) # dbg
 
             # if there is only a tab on a line with only whitespace, instead of
             # the mostly useless 'do you want to see all million completions'
             # message, just do the right thing and give the user his tab!
             # Incidentally, this enables pasting of tabbed text from an editor
             # (as long as autoindent is off).
 
             # It should be noted that at least pyreadline still shows file
             # completions - is there a way around it?
 
             # don't apply this on 'dumb' terminals, such as emacs buffers, so
             # we don't interfere with their own tab-completion mechanism.
             if not (self.dumb_terminal or line_buffer.strip()):
                 self.readline.insert_text('\t')
                 sys.stdout.flush()
                 return None
 
             # Note: debugging exceptions that may occur in completion is very
             # tricky, because readline unconditionally silences them.  So if
             # during development you suspect a bug in the completion code, turn
             # this flag on temporarily by uncommenting the second form (don't
             # flip the value in the first line, as the '# dbg' marker can be
             # automatically detected and is used elsewhere).
             DEBUG = False
             #DEBUG = True # dbg
             if DEBUG:
                 try:
                     self.complete(text, line_buffer, cursor_pos)
                 except:
                     import traceback; traceback.print_exc()
             else:
                 # The normal production version is here
                 
                 # This method computes the self.matches array
                 self.complete(text, line_buffer, cursor_pos)
 
         try:
             return self.matches[state]
         except IndexError:
             return None