16.8. 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()
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:
- Parse and execute single line of a readline init file.
- Return the current contents of the line buffer.
- Insert text into the command line.
- Parse a readline initialization file. The default filename is the last filename
- Load a readline history file. The default filename is ~/.history.
- Save a readline history file. The default filename is ~/.history.
- Clear the current history. (Note: this function is not available if the
installed version of GNU readline doesn’t support it.)
- Return the desired length of the history file. Negative values imply unlimited
history file size.
- 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.
- 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.)
- Return the current contents of history item at index.
- Remove history item specified by its position from the history.
- Replace history item specified by its position with the given line.
- Change what’s displayed on the screen to reflect the current contents of the
- 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.
- 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.
- 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.
- Get the completer function, or None if no completer function has been set.
- Get the type of completion being attempted.
- Get the beginning index of the readline tab-completion scope.
- Get the ending index of the readline tab-completion scope.
- Set the readline word delimiters for tab-completion.
- Get the readline word delimiters for tab-completion.
- 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.
- Append a line to the history buffer, as if it was the last line typed.
- Module rlcompleter
- Completion of Python identifiers at the interactive prompt.
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
histfile = os.path.join(os.environ["HOME"], ".pyhist")
del os, histfile
The following example extends the code.InteractiveConsole class to
support history save/restore.
def __init__(self, locals=None, filename="<console>",
code.InteractiveConsole.__init__(self, locals, filename)
def init_history(self, histfile):
if hasattr(readline, "read_history_file"):
def save_history(self, histfile):