
``readline`` --- GNU readline interface
***************************************

Platform: Unix

*Platforms: *Unix

The ``readline`` module defines a number of functions to facilitate
completion and reading/writing of history files from the Python
interpreter. This module can be used directly or via the
``rlcompleter`` module.  Settings made using  this module affect the
behaviour of both the interpreter's interactive prompt  and the
prompts offered by the ``raw_input()`` and ``input()`` built-in
functions.

..note:

   On MacOS X the :mod:`readline` module can be implemented using
   the ``libedit`` library instead of GNU readline.

   The configuration file for ``libedit`` is different from that
   of GNU readline. If you programmaticly load configuration strings
   you can check for the text "libedit" in :const:`readline.__doc__`
   to differentiate between GNU readline and libedit.

The ``readline`` module defines the following functions:

readline.parse_and_bind(string)

   Parse and execute single line of a readline init file.

readline.get_line_buffer()

   Return the current contents of the line buffer.

readline.insert_text(string)

   Insert text into the command line.

readline.read_init_file([filename])

   Parse a readline initialization file. The default filename is the
   last filename used.

readline.read_history_file([filename])

   Load a readline history file. The default filename is
   ``~/.history``.

readline.write_history_file([filename])

   Save a readline history file. The default filename is
   ``~/.history``.

readline.clear_history()

   Clear the current history.  (Note: this function is not available
   if the installed version of GNU readline doesn't support it.)

   New in version 2.4.

readline.get_history_length()

   Return the desired length of the history file.  Negative values
   imply unlimited history file size.

readline.set_history_length(length)

   Set the number of lines to save in the history file.
   ``write_history_file()`` uses this value to truncate the history
   file when saving.  Negative values imply unlimited history file
   size.

readline.get_current_history_length()

   Return the number of lines currently in the history.  (This is
   different from ``get_history_length()``, which returns the maximum
   number of lines that will be written to a history file.)

   New in version 2.3.

readline.get_history_item(index)

   Return the current contents of history item at *index*.

   New in version 2.3.

readline.remove_history_item(pos)

   Remove history item specified by its position from the history.

   New in version 2.4.

readline.replace_history_item(pos, line)

   Replace history item specified by its position with the given line.

   New in version 2.4.

readline.redisplay()

   Change what's displayed on the screen to reflect the current
   contents of the line buffer.

   New in version 2.3.

readline.set_startup_hook([function])

   Set or remove the startup_hook function.  If *function* is
   specified, it will be used as the new startup_hook function; if
   omitted or ``None``, any hook function already installed is
   removed.  The startup_hook function is called with no arguments
   just before readline prints the first prompt.

readline.set_pre_input_hook([function])

   Set or remove the pre_input_hook function.  If *function* is
   specified, it will be used as the new pre_input_hook function; if
   omitted or ``None``, any hook function already installed is
   removed.  The pre_input_hook function is called with no arguments
   after the first prompt has been printed and just before readline
   starts reading input characters.

readline.set_completer([function])

   Set or remove the completer function.  If *function* is specified,
   it will be used as the new completer function; if omitted or
   ``None``, any completer function already installed is removed.  The
   completer function is called as ``function(text, state)``, for
   *state* in ``0``, ``1``, ``2``, ..., until it returns a non-string
   value.  It should return the next possible completion starting with
   *text*.

readline.get_completer()

   Get the completer function, or ``None`` if no completer function
   has been set.

   New in version 2.3.

readline.get_completion_type()

   Get the type of completion being attempted.

   New in version 2.6.

readline.get_begidx()

   Get the beginning index of the readline tab-completion scope.

readline.get_endidx()

   Get the ending index of the readline tab-completion scope.

readline.set_completer_delims(string)

   Set the readline word delimiters for tab-completion.

readline.get_completer_delims()

   Get the readline word delimiters for tab-completion.

readline.set_completion_display_matches_hook([function])

   Set or remove the completion display function.  If *function* is
   specified, it will be used as the new completion display function;
   if omitted or ``None``, any completion display function already
   installed is removed.  The completion display function is called as
   ``function(substitution, [matches], longest_match_length)`` once
   each time matches need to be displayed.

   New in version 2.6.

readline.add_history(line)

   Append a line to the history buffer, as if it was the last line
   typed.

See also:

   Module ``rlcompleter``
      Completion of Python identifiers at the interactive prompt.


Example
=======

The following example demonstrates how to use the ``readline``
module's history reading and writing functions to automatically load
and save a history file named ``.pyhist`` from the user's home
directory.  The code below would normally be executed automatically
during interactive sessions from the user's **PYTHONSTARTUP** file.

   import os
   histfile = os.path.join(os.environ["HOME"], ".pyhist")
   try:
       readline.read_history_file(histfile)
   except IOError:
       pass
   import atexit
   atexit.register(readline.write_history_file, histfile)
   del os, histfile

The following example extends the ``code.InteractiveConsole`` class to
support history save/restore.

   import code
   import readline
   import atexit
   import os

   class HistoryConsole(code.InteractiveConsole):
       def __init__(self, locals=None, filename="<console>",
                    histfile=os.path.expanduser("~/.console-history")):
           code.InteractiveConsole.__init__(self, locals, filename)
           self.init_history(histfile)

       def init_history(self, histfile):
           readline.parse_and_bind("tab: complete")
           if hasattr(readline, "read_history_file"):
               try:
                   readline.read_history_file(histfile)
               except IOError:
                   pass
               atexit.register(self.save_history, histfile)

       def save_history(self, histfile):
           readline.write_history_file(histfile)
