:mod:!readline --- GNU readline interface

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

The :mod:!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 :mod:rlcompleter module, which supports completion of Python identifiers at the interactive prompt. Settings made using this module affect the behaviour of both the interpreter's interactive prompt and the prompts offered by the built-in :func:input function.

Readline keybindings may be configured via an initialization file, typically .inputrc in your home directory. See Readline Init File <https://tiswww.cwru.edu/php/chet/readline/rluserman.html#Readline-Init-File>_ in the GNU Readline manual for information about the format and allowable constructs of that file, and the capabilities of the Readline library in general.

.. include:: ../includes/wasm-mobile-notavail.rst

.. include:: ../includes/optional-module.rst

.. availability:: Unix.

.. note::

The underlying Readline library API may be implemented by the editline (libedit) library instead of GNU readline. On macOS the :mod:!readline module detects which library is being used at run time.

The configuration file for editline is different from that of GNU readline. If you programmatically load configuration strings you can use :data:backend to determine which library is being used.

If you use editline/libedit readline emulation on macOS, the initialization file located in your home directory is named .editrc. For example, the following content in ~/.editrc will turn ON vi keybindings and TAB completion::

python:bind -v
python:bind ^I rl_complete

Also note that different libraries may use different history file formats. When switching the underlying library, existing history files may become unusable.

.. data:: backend

The name of the underlying Readline library being used, either "readline" or "editline".

.. versionadded:: 3.13

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. It raises an :ref:auditing event <auditing> open with the file name if given, and :code:"<readline_init_file>" otherwise, regardless of which file the library resolves.

.. versionchanged:: 3.14 The auditing event was added.

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 and raises an :ref:auditing event <auditing> open with the file name if given and :code:"~/.history" otherwise.

.. versionchanged:: 3.14 The auditing event was added.

.. 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 and raises an :ref:auditing event <auditing> open with the file name if given and :code:"~/.history" otherwise.

.. versionchanged:: 3.14 The auditing event was added.

.. 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. It raises an :ref:auditing event <auditing> open with the file name if given and :code:"~/.history" otherwise.

.. versionadded:: 3.5

.. versionchanged:: 3.14 The auditing event was added.

.. 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.

.. function:: get_pre_input_hook()

Get the current pre-input hook function, or None if no pre-input hook function has been set. This function only exists if Python was compiled for a version of the library that supports it.

.. versionadded:: 3.15

.. _readline-completion:

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. The values may be different in the same input editing scenario based on the underlying C readline implementation. Ex: libedit is known to behave differently than libreadline.

.. 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.

.. _readline-example:

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)

.. note::

The new :term:REPL introduced in version 3.13 doesn't support readline. However, readline can still be used by setting the :envvar:PYTHON_BASIC_REPL environment variable.