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16.8. 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 raw_input()
and input()
built-in functions.
Note
The underlying Readline library API may be implemented by the libedit
library instead of GNU readline. On MacOS X 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 readline.__doc__
to differentiate between GNU readline and libedit.
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.
16.8.1. Init file
The following functions relate to the init file and user configuration:
16.8.2. 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).
16.8.3. 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 callsread_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 callswrite_history()
in the underlying library.
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 callinghistory_truncate_file()
in the underlying library. Negative values imply unlimited history file size.
16.8.4. History list
The following functions operate on a global history list:
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.New in version 2.4.
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.)New in version 2.3.
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.New in version 2.3.
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.New in version 2.4.
16.8.5. Startup hooks
New in version 2.3.
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 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 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 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.
16.8.6. 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 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 ] )-
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 asfunction(text, state)
, for state in0
,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
rl_completion_matches()
in the underlying library. The text string comes from the first parameter to therl_attempted_completion_function
callback of the underlying library.
readline.
get_completer
( )-
Get the completer function, or
None
if no completer function has been set.New in version 2.3.
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.New in version 2.6.
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.
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 therl_completion_display_matches_hook
callback in the underlying library. The completion display function is called asfunction(substitution, [matches], longest_match_length)
once each time matches need to be displayed.New in version 2.6.
16.8.7. Example
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 .pyhist
from the user’s home directory. The code below would normally be executed automatically during interactive sessions from the user’s PYTHONSTARTUP
file.
import os
import readline
histfile = os.path.join(os.path.expanduser("~"), ".pyhist")
try:
readline.read_history_file(histfile)
# default history len is -1 (infinite), which may grow unruly
readline.set_history_length(1000)
except IOError:
pass
import atexit
atexit.register(readline.write_history_file, histfile)
del os, histfile
The following example extends the code.InteractiveConsole
class to support history save/restore.
import code
import readline
import atexit
import os
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 IOError:
pass
atexit.register(self.save_history, histfile)
def save_history(self, histfile):
readline.set_history_length(1000)
readline.write_history_file(histfile)