readline — GNU readline interface¶
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
Readline keybindings may be configured via an initialization file, typically
.inputrc in your home directory. See 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.
The underlying Readline library API may be implemented by
libedit library instead of GNU readline.
On macOS the
readline module detects which library is being used
at run time.
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
to differentiate between GNU readline and libedit.
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
turn ON vi keybindings and TAB completion:
python:bind -v python:bind ^I rl_complete
The following functions relate to the init file and user configuration:
Execute the init line provided in the string argument. This calls
rl_parse_and_bind()in the underlying library.
Execute a readline initialization file. The default filename is the last filename used. This calls
rl_read_init_file()in the underlying library.
The following functions operate on the line buffer:
Return the current contents of the line buffer (
rl_line_bufferin the underlying library).
Insert text into the line buffer at the cursor position. This calls
rl_insert_text()in the underlying library, but ignores the return value.
Change what’s displayed on the screen to reflect the current contents of the line buffer. This calls
rl_redisplay()in the underlying library.
The following functions operate on a history file:
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.
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.
- 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.
New in version 3.5.
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.
The following functions operate on a global history list:
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.
Return the number of items 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. The item index is one-based. This calls
history_get()in the underlying library.
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.
Append line to the history buffer, as if it was the last line typed. This calls
add_history()in the underlying library.
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.
New in version 3.6.
CPython implementation detail: Auto history is enabled by default, and changes to this do not persist across multiple sessions.
Set or remove the function invoked by the
rl_startup_hookcallback 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.
Set or remove the function invoked by the
rl_pre_input_hookcallback 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.
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.
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
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
rl_completion_matches()in the underlying library. The text string comes from the first parameter to the
rl_attempted_completion_functioncallback of the underlying library.
Get the completer function, or
Noneif no completer function has been set.
Get the type of completion being attempted. This returns the
rl_completion_typevariable in the underlying library as an integer.
Get the beginning or ending index of the completion scope. These indexes are the start and end arguments passed to the
rl_attempted_completion_functioncallback 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.
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_charactersvariable in the underlying library.
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_hookcallback 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.
The following example demonstrates how to use the
history reading and writing functions to automatically load and save a history
.python_history from the user’s home directory. The code
below would normally be executed automatically during interactive sessions
from the user’s
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 interactive mode (see Readline configuration).
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
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)