readline— GNU readline interface

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Thereadlinemodule 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 therlcompletermodule, 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-ininput() function.

Readline keybindings may be configured via an initialization file, typically .inputrcin your home directory. SeeReadline 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.

Note

The underlying Readline library API may be implemented by thelibeditlibrary instead of GNU readline. On macOS thereadlinemodule detects which library is being used at run time.

The configuration file forlibeditis different from that of GNU readline. If you programmatically load configuration strings you can check for the text “libedit” inreadline.__doc__ to differentiate between GNU readline and libedit.

If you useeditline/libeditreadline emulation on macOS, the initialization file located in your home directory is named .editrc.For example, the following content in~/.editrcwill turn ONvikeybindings and TAB completion:

Python:bind-v
Python:bind^Irl_complete

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

Init file

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

readline.parse_and_bind(string)

Execute the init line provided in thestringargument. 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 callsrl_read_init_file()in the underlying library.

Line buffer

The following functions operate on the line buffer:

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 callsrl_redisplay()in the underlying library.

History file

The following functions operate on a history file:

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.

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.

readline.append_history_file(nelements[,filename])

Append the lastnelementsitems 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.

Added in version 3.5.

readline.get_history_length()

readline.set_history_length(length)

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

History list

The following functions operate on a global history list:

readline.clear_history()

Clear the current history. This callsclear_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()

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.)

readline.get_history_item(index)

Return the current contents of history item atindex.The item index is one-based. This callshistory_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 callsremove_history()in the underlying library.

readline.replace_history_item(pos,line)

Replace history item specified by its position withline. The position is zero-based. This callsreplace_history_entry() in the underlying library.

readline.add_history(line)

Appendlineto the history buffer, as if it was the last line typed. This callsadd_history()in the underlying library.

readline.set_auto_history(enabled)

Enable or disable automatic calls toadd_history()when reading input via readline. Theenabledargument should be a Boolean value that when true, enables auto history, and that when false, disables auto history.

Added in version 3.6.

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

Startup hooks

readline.set_startup_hook([function])

Set or remove the function invoked by therl_startup_hook callback of the underlying library. Iffunctionis specified, it will be used as the new hook function; if omitted orNone,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 therl_pre_input_hook callback of the underlying library. Iffunctionis specified, it will be used as the new hook function; if omitted orNone,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 byrlcompleterto complete Python identifiers for the interactive interpreter. If thereadlinemodule is to be used with a custom completer, a different set of word delimiters should be set.

readline.set_completer([function])

Set or remove the completer function. Iffunctionis specified, it will be used as the new completer function; if omitted orNone,any completer function already installed is removed. The completer function is called as function(text,state),forstatein0,1,2,…, until it returns a non-string value. It should return the next possible completion starting withtext.

The installed completer function is invoked by theentry_funccallback passed torl_completion_matches()in the underlying library. Thetextstring comes from the first parameter to the rl_attempted_completion_functioncallback of the underlying library.

readline.get_completer()

Get the completer function, orNoneif no completer function has been set.

readline.get_completion_type()

Get the type of completion being attempted. This returns the rl_completion_typevariable 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 thestartandendarguments 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.

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 therl_completer_word_break_characters variable in the underlying library.

readline.set_completion_display_matches_hook([function])

Set or remove the completion display function. Iffunctionis specified, it will be used as the new completion display function; if omitted orNone,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.

Example

The following example demonstrates how to use thereadlinemodule’s history reading and writing functions to automatically load and save a history file named.Python _historyfrom the user’s home directory. The code below would normally be executed automatically during interactive sessions from the user’sPYTHONSTARTUPfile.

importatexit
importos
importreadline

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)
exceptFileNotFoundError:
pass

atexit.register(readline.write_history_file,histfile)

This code is actually automatically run when Python is run in interactive mode(seeReadline configuration).

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

importatexit
importos
importreadline
histfile=os.path.join(os.path.expanduser("~"),".Python _history")

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

defsave(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 thecode.InteractiveConsoleclass to support history save/restore.

importatexit
importcode
importos
importreadline

classHistoryConsole(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)

definit_history(self,histfile):
readline.parse_and_bind("tab: complete")
ifhasattr(readline,"read_history_file"):
try:
readline.read_history_file(histfile)
exceptFileNotFoundError:
pass
atexit.register(self.save_history,histfile)

defsave_history(self,histfile):
readline.set_history_length(1000)
readline.write_history_file(histfile)