# `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, 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 `input()` function.

Las combinaciones de teclas de Readline se pueden configurar mediante un archivo de inicialización, generalmente `.inputrc` en su directorio de inicio. Consulte Readline Init File en el manual de GNU Readline para obtener información sobre el formato y las construcciones permitidas de ese archivo, y las capacidades de la biblioteca Readline en general.

Availability: not Android, not iOS, not WASI.

This module is not supported on mobile platforms or WebAssembly platforms.

This is an optional module. If it is missing from your copy of CPython, look for documentation from your distributor (that is, whoever provided Python to you). If you are the distributor, see Requirements for optional modules.

Nota

The underlying Readline library API may be implemented by the `editline` (`libedit`) library instead of GNU readline. On macOS the `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 `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.

readline.backend

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

  Added in version 3.13.

## Archivo de inicio

Las siguientes funciones se relacionan con el archivo de inicio y la configuración del usuario:

readline.parse_and_bind(string)

  Execute the init line provided in the string argument. This calls `rl_parse_and_bind()` in the underlying library.

readline.read_init_file([filename])

  Execute a readline initialization file. The default filename is the last filename used. This calls `rl_read_init_file()` in the underlying library. It raises an auditing event `open` with the file name if given, and `"<readline_init_file>"` otherwise, regardless of which file the library resolves.

  Distinto en la versión 3.14: The auditing event was added.

## Búfer de línea

Las siguientes funciones operan en el búfer de línea:

readline.get_line_buffer()

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

readline.insert_text(string)

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

readline.redisplay()

  Change what’s displayed on the screen to reflect the current contents of the line buffer. This calls `rl_redisplay()` in the underlying library.

## Archivo de historial

Las siguientes funciones operan en un archivo de historial:

readline.read_history_file([filename])

  Load a readline history file, and append it to the history list. The default filename is `~/.history`. This calls `read_history()` in the underlying library and raises an auditing event `open` with the file name if given and `"~/.history"` otherwise.

  Distinto en la versión 3.14: The auditing event was added.

readline.write_history_file([filename])

  Save the history list to a readline history file, overwriting any existing file. The default filename is `~/.history`. This calls `write_history()` in the underlying library and raises an auditing event `open` with the file name if given and `"~/.history"` otherwise.

  Distinto en la versión 3.14: The auditing event was added.

readline.append_history_file(nelements[, filename])

  Append the last nelements items of history to a file. The default filename is `~/.history`. The file must already exist. This calls `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 auditing event `open` with the file name if given and `"~/.history"` otherwise.

  Added in version 3.5.

  Distinto en la versión 3.14: The auditing event was added.

readline.get_history_length()
readline.set_history_length(length)

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

## Lista del historial

Las siguientes funciones operan en una lista de historial global:

readline.clear_history()

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

readline.get_current_history_length()

  Retorna el número de elementos actuales en el historial. (Esto es diferente de la función `get_history_length()`, que retorna el número máximo de líneas que se escribirán en un archivo de historial).

readline.get_history_item(index)

  Return the current contents of history item at index. The item index is one-based. This calls `history_get()` in the underlying library.

readline.remove_history_item(pos)

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

readline.replace_history_item(pos, line)

  Replace history item specified by its position with line. The position is zero-based. This calls `replace_history_entry()` in the underlying library.

readline.add_history(line)

  Append line to the history buffer, as if it was the last line typed. This calls `add_history()` in the underlying library.

readline.set_auto_history(enabled)

  Enable or disable automatic calls to `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.

  Added in version 3.6.

  Auto history está habilitado de forma predeterminada, y cambiarlo no hará que persista en múltiples sesiones.

## Ganchos (hooks) de inicialización

readline.set_startup_hook([function])

  Set or remove the function invoked by the `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.

readline.set_pre_input_hook([function])

  Set or remove the function invoked by the `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.

readline.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.

  Added in version 3.15.

## Terminación

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 `rlcompleter` to complete Python identifiers for the interactive interpreter. If the `readline` module is to be used with a custom completer, a different set of word delimiters should be set.

readline.set_completer([function])

  Establece o elimina la función de finalización. Si se especifica function, se usará como la nueva función de finalización; Si se omite o es `None`, se elimina cualquier función de finalización ya instalada. La función completa se llama como `function(text, state)`, para state en `0`, `1`, `2`, …, hasta que retorna un valor que no es una cadena de caracteres. Debería retornar las siguientes terminaciones posibles comenzando con text.

  The installed completer function is invoked by the entry_func callback passed to `rl_completion_matches()` in the underlying library. The text string comes from the first parameter to the `rl_attempted_completion_function` callback of the underlying library.

readline.get_completer()

  Obtiene la función de finalización o `None` si no se ha definido ninguna función de finalización.

readline.get_completion_type()

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

readline.get_begidx()
readline.get_endidx()

  Get the beginning or ending index of the completion scope. These indexes are the start and end arguments passed to the `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.

readline.set_completer_delims(string)
readline.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 `rl_completer_word_break_characters` variable in the underlying library.

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. This sets or clears the `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.

## Ejemplo

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)
        # 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)

Este código se ejecuta automáticamente cuando Python se ejecuta en modo interactivo (ver Configuración de Readline).

El siguiente ejemplo logra el mismo objetivo pero administra sesiones interactivas concurrentes, agregando solo el nuevo historial.

    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)

El siguiente ejemplo amplía la clase `code.InteractiveConsole` para administrar el guardado/restauración del historial.

    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)

Nota

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