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360 lines
12 KiB
360 lines
12 KiB
:mod:`readline` --- GNU readline interface
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==========================================
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.. module:: readline
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:platform: Unix
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:synopsis: GNU readline support for Python.
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.. sectionauthor:: Skip Montanaro <skip@pobox.com>
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--------------
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The :mod:`readline` module defines a number of functions to facilitate
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completion and reading/writing of history files from the Python interpreter.
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This module can be used directly, or via the :mod:`rlcompleter` module, which
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supports completion of Python identifiers at the interactive prompt. Settings
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made using this module affect the behaviour of both the interpreter's
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interactive prompt and the prompts offered by the built-in :func:`input`
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function.
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Readline keybindings may be configured via an initialization file, typically
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``.inputrc`` in your home directory. See `Readline Init File
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<https://tiswww.cwru.edu/php/chet/readline/rluserman.html#SEC9>`_
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in the GNU Readline manual for information about the format and
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allowable constructs of that file, and the capabilities of the
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Readline library in general.
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.. note::
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The underlying Readline library API may be implemented by
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the ``libedit`` library instead of GNU readline.
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On macOS the :mod:`readline` module detects which library is being used
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at run time.
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The configuration file for ``libedit`` is different from that
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of GNU readline. If you programmatically load configuration strings
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you can check for the text "libedit" in :const:`readline.__doc__`
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to differentiate between GNU readline and libedit.
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If you use *editline*/``libedit`` readline emulation on macOS, the
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initialization file located in your home directory is named
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``.editrc``. For example, the following content in ``~/.editrc`` will
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turn ON *vi* keybindings and TAB completion::
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python:bind -v
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python:bind ^I rl_complete
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Init file
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---------
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The following functions relate to the init file and user configuration:
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.. function:: parse_and_bind(string)
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Execute the init line provided in the *string* argument. This calls
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:c:func:`rl_parse_and_bind` in the underlying library.
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.. function:: read_init_file([filename])
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Execute a readline initialization file. The default filename is the last filename
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used. This calls :c:func:`rl_read_init_file` in the underlying library.
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Line buffer
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-----------
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The following functions operate on the line buffer:
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.. function:: get_line_buffer()
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Return the current contents of the line buffer (:c:data:`rl_line_buffer`
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in the underlying library).
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.. function:: insert_text(string)
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Insert text into the line buffer at the cursor position. This calls
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:c:func:`rl_insert_text` in the underlying library, but ignores
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the return value.
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.. function:: redisplay()
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Change what's displayed on the screen to reflect the current contents of the
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line buffer. This calls :c:func:`rl_redisplay` in the underlying library.
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History file
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------------
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The following functions operate on a history file:
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.. function:: read_history_file([filename])
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Load a readline history file, and append it to the history list.
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The default filename is :file:`~/.history`. This calls
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:c:func:`read_history` in the underlying library.
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.. function:: write_history_file([filename])
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Save the history list to a readline history file, overwriting any
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existing file. The default filename is :file:`~/.history`. This calls
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:c:func:`write_history` in the underlying library.
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.. function:: append_history_file(nelements[, filename])
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Append the last *nelements* items of history to a file. The default filename is
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:file:`~/.history`. The file must already exist. This calls
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:c:func:`append_history` in the underlying library. This function
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only exists if Python was compiled for a version of the library
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that supports it.
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.. versionadded:: 3.5
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.. function:: get_history_length()
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set_history_length(length)
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Set or return the desired number of lines to save in the history file.
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The :func:`write_history_file` function uses this value to truncate
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the history file, by calling :c:func:`history_truncate_file` in
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the underlying library. Negative values imply
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unlimited history file size.
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History list
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------------
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The following functions operate on a global history list:
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.. function:: clear_history()
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Clear the current history. This calls :c:func:`clear_history` in the
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underlying library. The Python function only exists if Python was
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compiled for a version of the library that supports it.
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.. function:: get_current_history_length()
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Return the number of items currently in the history. (This is different from
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:func:`get_history_length`, which returns the maximum number of lines that will
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be written to a history file.)
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.. function:: get_history_item(index)
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Return the current contents of history item at *index*. The item index
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is one-based. This calls :c:func:`history_get` in the underlying library.
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.. function:: remove_history_item(pos)
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Remove history item specified by its position from the history.
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The position is zero-based. This calls :c:func:`remove_history` in
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the underlying library.
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.. function:: replace_history_item(pos, line)
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Replace history item specified by its position with *line*.
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The position is zero-based. This calls :c:func:`replace_history_entry`
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in the underlying library.
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.. function:: add_history(line)
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Append *line* to the history buffer, as if it was the last line typed.
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This calls :c:func:`add_history` in the underlying library.
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.. function:: set_auto_history(enabled)
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Enable or disable automatic calls to :c:func:`add_history` when reading
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input via readline. The *enabled* argument should be a Boolean value
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that when true, enables auto history, and that when false, disables
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auto history.
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.. versionadded:: 3.6
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.. impl-detail::
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Auto history is enabled by default, and changes to this do not persist
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across multiple sessions.
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Startup hooks
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-------------
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.. function:: set_startup_hook([function])
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Set or remove the function invoked by the :c:data:`rl_startup_hook`
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callback of the underlying library. If *function* is specified, it will
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be used as the new hook function; if omitted or ``None``, any function
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already installed is removed. The hook is called with no
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arguments just before readline prints the first prompt.
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.. function:: set_pre_input_hook([function])
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Set or remove the function invoked by the :c:data:`rl_pre_input_hook`
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callback of the underlying library. If *function* is specified, it will
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be used as the new hook function; if omitted or ``None``, any
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function already installed is removed. The hook is called
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with no arguments after the first prompt has been printed and just before
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readline starts reading input characters. This function only exists
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if Python was compiled for a version of the library that supports it.
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Completion
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----------
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The following functions relate to implementing a custom word completion
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function. This is typically operated by the Tab key, and can suggest and
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automatically complete a word being typed. By default, Readline is set up
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to be used by :mod:`rlcompleter` to complete Python identifiers for
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the interactive interpreter. If the :mod:`readline` module is to be used
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with a custom completer, a different set of word delimiters should be set.
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.. function:: set_completer([function])
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Set or remove the completer function. If *function* is specified, it will be
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used as the new completer function; if omitted or ``None``, any completer
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function already installed is removed. The completer function is called as
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``function(text, state)``, for *state* in ``0``, ``1``, ``2``, ..., until it
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returns a non-string value. It should return the next possible completion
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starting with *text*.
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The installed completer function is invoked by the *entry_func* callback
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passed to :c:func:`rl_completion_matches` in the underlying library.
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The *text* string comes from the first parameter to the
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:c:data:`rl_attempted_completion_function` callback of the
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underlying library.
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.. function:: get_completer()
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Get the completer function, or ``None`` if no completer function has been set.
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.. function:: get_completion_type()
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Get the type of completion being attempted. This returns the
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:c:data:`rl_completion_type` variable in the underlying library as
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an integer.
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.. function:: get_begidx()
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get_endidx()
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Get the beginning or ending index of the completion scope.
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These indexes are the *start* and *end* arguments passed to the
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:c:data:`rl_attempted_completion_function` callback of the
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underlying library.
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.. function:: set_completer_delims(string)
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get_completer_delims()
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Set or get the word delimiters for completion. These determine the
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start of the word to be considered for completion (the completion scope).
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These functions access the :c:data:`rl_completer_word_break_characters`
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variable in the underlying library.
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.. function:: set_completion_display_matches_hook([function])
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Set or remove the completion display function. If *function* is
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specified, it will be used as the new completion display function;
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if omitted or ``None``, any completion display function already
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installed is removed. This sets or clears the
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:c:data:`rl_completion_display_matches_hook` callback in the
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underlying library. The completion display function is called as
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``function(substitution, [matches], longest_match_length)`` once
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each time matches need to be displayed.
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.. _readline-example:
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Example
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-------
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The following example demonstrates how to use the :mod:`readline` module's
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history reading and writing functions to automatically load and save a history
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file named :file:`.python_history` from the user's home directory. The code
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below would normally be executed automatically during interactive sessions
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from the user's :envvar:`PYTHONSTARTUP` file. ::
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import atexit
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import os
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import readline
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histfile = os.path.join(os.path.expanduser("~"), ".python_history")
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try:
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readline.read_history_file(histfile)
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# default history len is -1 (infinite), which may grow unruly
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readline.set_history_length(1000)
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except FileNotFoundError:
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pass
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atexit.register(readline.write_history_file, histfile)
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This code is actually automatically run when Python is run in
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:ref:`interactive mode <tut-interactive>` (see :ref:`rlcompleter-config`).
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The following example achieves the same goal but supports concurrent interactive
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sessions, by only appending the new history. ::
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import atexit
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import os
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import readline
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histfile = os.path.join(os.path.expanduser("~"), ".python_history")
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try:
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readline.read_history_file(histfile)
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h_len = readline.get_current_history_length()
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except FileNotFoundError:
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open(histfile, 'wb').close()
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h_len = 0
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def save(prev_h_len, histfile):
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new_h_len = readline.get_current_history_length()
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readline.set_history_length(1000)
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readline.append_history_file(new_h_len - prev_h_len, histfile)
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atexit.register(save, h_len, histfile)
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The following example extends the :class:`code.InteractiveConsole` class to
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support history save/restore. ::
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import atexit
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import code
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import os
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import readline
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class HistoryConsole(code.InteractiveConsole):
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def __init__(self, locals=None, filename="<console>",
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histfile=os.path.expanduser("~/.console-history")):
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code.InteractiveConsole.__init__(self, locals, filename)
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self.init_history(histfile)
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def init_history(self, histfile):
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readline.parse_and_bind("tab: complete")
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if hasattr(readline, "read_history_file"):
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try:
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readline.read_history_file(histfile)
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except FileNotFoundError:
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pass
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atexit.register(self.save_history, histfile)
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def save_history(self, histfile):
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readline.set_history_length(1000)
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readline.write_history_file(histfile)
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