Replace lowercase ASCII characters with X in Python [duplicate]

I'd use str.translate() for that; easily the fastest method. A regular expression cannot touch this for speed.

Python 2 version:

import string map = string.maketrans(string.ascii_lowercase, 'X' * len(string.ascii_lowercase)) mapped = inputstring.translate(map) 

Python 3 version:

import string map = str.maketrans(dict.fromkeys(string.ascii_lowercase, 'X')) mapped = inputstring.translate(map) 

Demo (Python 2):

>>> import string >>> inputstring = 'ABCDEFGhijklmnopQRSTUVwxyz' >>> map = string.maketrans(string.ascii_lowercase, 'X' * len(string.ascii_lowercase)) >>> inputstring.translate(map) 'ABCDEFGXXXXXXXXXQRSTUVXXXX' 

str.translate() is orders of magniture faster here:

>>> import timeit >>> import re >>> def regex_replace(s, _sub=re.compile(r'[a-z]').sub): ... return _sub('X', s) ... >>> regex_replace(inputstring) 'ABCDEFGXXXXXXXXXQRSTUVXXXX' >>> timeit.timeit('f(s)', 'from __main__ import regex_replace as f, inputstring as s') 2.6076979637145996 >>> timeit.timeit('s.translate(m)', 'from __main__ import inputstring as s, map as m') 0.13378620147705078 

The str.translate() version manages to do the task 20 times faster.

You can use regex:

import re output = re.sub( r'[a-z]', 'X', inputString )