Python GNU readline Interface

The readline is UNIX specific module. It defines a number of functions to read and write history files in easier way from python interpreter. We can use this module directly or using the rlcompleter module. This module settings may affect the built-in input() method prompt and also the interactive prompt.

For the MAC based system (on MAC OS X) this readline module can be implemented using the libedit library. The libedit configuration is different from GNU readline.

To use this module, we need to import the readline module in the python code

import readline

Some methods of GNU readline are as follows −

This code is used to read the history file and store it inside the home directory. The code will work when it is compiled and run in interactive mode. After exiting the python shell, it will store the history file.

Example Code

import readline as rl
import os
import atexit

my_hist_file = os.path.join(os.path.expanduser("~"), ".my_python_hist")
try:
   rl.read_history_file(my_hist_file)
   rl.clear_history()
except FileNotFoundError:
   pass
    
print("Done")
atexit.register(rl.write_history_file, my_hist_file)
del os, my_hist_file

Run in interactive shell −

$ python3
Python 3.6.5 (default, Apr  1 2018, 05:46:30)
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> exec(open("./readline_task.py").read())
Done
>>> print("readline_task.py is ececuted")
readline_task.py is ececuted
>>> print("History File will be updated after exit.")
History File will be updated after exit.
>>> 2 ** 10
1024
>>> 2 ** 20
1048576
>>> 2 ** 30
1073741824
>>> import math
>>> math.factorial(6)
720
>>> exit()
$ cat ~/.my_python_hist
print("readline_task.py is ececuted")
print("History File will be updated after exit.")
2 ** 10
2 ** 20
2 ** 30
import math
math.factorial(6)
exit()
$