:mod:`readline` --- GNU readline interface

.. module:: readline
 :platform: Unix
 :synopsis: GNU readline support for Python.

.. sectionauthor:: Skip Montanaro <skip@pobox.com>

python:bind -v
python:bind ^I rl_complete

Init file

The following functions relate to the init file and user configuration:

.. function:: parse_and_bind(string)

 Execute the init line provided in the *string* argument. This calls
 :c:func:`rl_parse_and_bind` in the underlying library.

.. function:: read_init_file([filename])

 Execute a readline initialization file. The default filename is the last filename
 used. This calls :c:func:`rl_read_init_file` in the underlying library.

Line buffer

The following functions operate on the line buffer:

.. function:: get_line_buffer()

 Return the current contents of the line buffer (:c:data:`rl_line_buffer`
 in the underlying library).

.. function:: insert_text(string)

 Insert text into the line buffer at the cursor position. This calls
 :c:func:`rl_insert_text` in the underlying library, but ignores
 the return value.

.. function:: redisplay()

 Change what's displayed on the screen to reflect the current contents of the
 line buffer. This calls :c:func:`rl_redisplay` in the underlying library.

History file

The following functions operate on a history file:

.. function:: read_history_file([filename])

 Load a readline history file, and append it to the history list.
 The default filename is :file:`~/.history`. This calls
 :c:func:`read_history` in the underlying library.

.. function:: write_history_file([filename])

 Save the history list to a readline history file, overwriting any
 existing file. The default filename is :file:`~/.history`. This calls
 :c:func:`write_history` in the underlying library.

.. function:: append_history_file(nelements[, filename])

 Append the last *nelements* items of history to a file. The default filename is
 :file:`~/.history`. The file must already exist. This calls
 :c:func:`append_history` in the underlying library. This function
 only exists if Python was compiled for a version of the library
 that supports it.

 .. versionadded:: 3.5

.. function:: get_history_length()
 set_history_length(length)

 Set or return the desired number of lines to save in the history file.
 The :func:`write_history_file` function uses this value to truncate
 the history file, by calling :c:func:`history_truncate_file` in
 the underlying library. Negative values imply
 unlimited history file size.

History list

The following functions operate on a global history list:

.. function:: clear_history()

 Clear the current history. This calls :c:func:`clear_history` in the
 underlying library. The Python function only exists if Python was
 compiled for a version of the library that supports it.

.. function:: get_current_history_length()

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

.. function:: get_history_item(index)

 Return the current contents of history item at *index*. The item index
 is one-based. This calls :c:func:`history_get` in the underlying library.

.. function:: remove_history_item(pos)

 Remove history item specified by its position from the history.
 The position is zero-based. This calls :c:func:`remove_history` in
 the underlying library.

.. function:: replace_history_item(pos, line)

 Replace history item specified by its position with *line*.
 The position is zero-based. This calls :c:func:`replace_history_entry`
 in the underlying library.

.. function:: add_history(line)

 Append *line* to the history buffer, as if it was the last line typed.
 This calls :c:func:`add_history` in the underlying library.

.. function:: set_auto_history(enabled)

 Enable or disable automatic calls to :c:func:`add_history` when reading
 input via readline. The *enabled* argument should be a Boolean value
 that when true, enables auto history, and that when false, disables
 auto history.

 .. versionadded:: 3.6

 .. impl-detail::
 Auto history is enabled by default, and changes to this do not persist
 across multiple sessions.

Startup hooks

.. function:: set_startup_hook([function])

 Set or remove the function invoked by the :c:data:`rl_startup_hook`
 callback of the underlying library. If *function* is specified, it will
 be used as the new hook function; if omitted or ``None``, any function
 already installed is removed. The hook is called with no
 arguments just before readline prints the first prompt.

.. function:: set_pre_input_hook([function])

 Set or remove the function invoked by the :c:data:`rl_pre_input_hook`
 callback of the underlying library. If *function* is specified, it will
 be used as the new hook function; if omitted or ``None``, any
 function already installed is removed. The hook is called
 with no arguments after the first prompt has been printed and just before
 readline starts reading input characters. This function only exists
 if Python was compiled for a version of the library that supports it.

Completion

The following functions relate to implementing a custom word completion function. This is typically operated by the Tab key, and can suggest and automatically complete a word being typed. By default, Readline is set up to be used by :mod:`rlcompleter` to complete Python identifiers for the interactive interpreter. If the :mod:`readline` module is to be used with a custom completer, a different set of word delimiters should be set.

.. function:: 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*.

 The installed completer function is invoked by the *entry_func* callback
 passed to :c:func:`rl_completion_matches` in the underlying library.
 The *text* string comes from the first parameter to the
 :c:data:`rl_attempted_completion_function` callback of the
 underlying library.

.. function:: get_completer()

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

.. function:: get_completion_type()

 Get the type of completion being attempted. This returns the
 :c:data:`rl_completion_type` variable in the underlying library as
 an integer.

.. function:: get_begidx()
 get_endidx()

 Get the beginning or ending index of the completion scope.
 These indexes are the *start* and *end* arguments passed to the
 :c:data:`rl_attempted_completion_function` callback of the
 underlying library.

.. function:: set_completer_delims(string)
 get_completer_delims()

 Set or get the word delimiters for completion. These determine the
 start of the word to be considered for completion (the completion scope).
 These functions access the :c:data:`rl_completer_word_break_characters`
 variable in the underlying library.

.. function:: 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. This sets or clears the
 :c:data:`rl_completion_display_matches_hook` callback in the
 underlying library. The completion display function is called as
 ``function(substitution, [matches], longest_match_length)`` once
 each time matches need to be displayed.

Example

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

import atexit
import os
import readline

histfile = os.path.join(os.path.expanduser("~"), ".python_history")
try:
 readline.read_history_file(histfile)
 # default history len is -1 (infinite), which may grow unruly
 readline.set_history_length(1000)
except FileNotFoundError:
 pass

atexit.register(readline.write_history_file, histfile)

This code is actually automatically run when Python is run in :ref:`interactive mode <tut-interactive>` (see :ref:`rlcompleter-config`).

The following example achieves the same goal but supports concurrent interactive sessions, by only appending the new history.

import atexit
import os
import readline
histfile = os.path.join(os.path.expanduser("~"), ".python_history")

try:
 readline.read_history_file(histfile)
 h_len = readline.get_current_history_length()
except FileNotFoundError:
 open(histfile, 'wb').close()
 h_len = 0

def save(prev_h_len, histfile):
 new_h_len = readline.get_current_history_length()
 readline.set_history_length(1000)
 readline.append_history_file(new_h_len - prev_h_len, histfile)
atexit.register(save, h_len, histfile)

The following example extends the :class:`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.set_history_length(1000)
 readline.write_history_file(histfile)

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