6.7. "readline" — GNU readline interface
****************************************

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
built-in "input()" function.

Note: On MacOS X the "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
  programmatically load configuration strings you can check for the
  text “libedit” in "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.)

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.)

readline.get_history_item(index)

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

readline.remove_history_item(pos)

   Remove history item specified by its position from the history.

readline.replace_history_item(pos, line)

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

readline.redisplay()

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

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.

readline.get_completion_type()

   Get the type of completion being attempted.

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.

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.


6.7.1. 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 ".python_history" from the user’s home directory.
The code below would normally be executed automatically during
interactive sessions from the user’s "PYTHONSTARTUP" file.

   import atexit
   import os
   import readline

   histfile = os.path.join(os.path.expanduser("~"), ".python_history")
   try:
       readline.read_history_file(histfile)
   except FileNotFoundError:
       pass

   atexit.register(readline.write_history_file, histfile)

This code is actually automatically run when Python is run in
interactive mode (see Readline configuration).

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

   import atexit
   import code
   import os
   import readline

   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 FileNotFoundError:
                   pass
               atexit.register(self.save_history, histfile)

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