Question

I am getting different results based on whether I precompile a regular expression:

>>> re.compile('mr', re.IGNORECASE).sub('', 'Mr Bean')
' Bean'
>>> re.sub('mr', '', 'Mr Bean', re.IGNORECASE)
'Mr Bean'

The Python documentation says Some of the functions are simplified versions of the full featured methods for compiled regular expressions. However it also claims RegexObject.sub() is Identical to the sub() function.

So what is going on here?

Answer 1

re.sub() can’t accept the re.IGNORECASE, it appears.

The documentation states:

sub(pattern, repl, string, count=0)

Return the string obtained by replacing the leftmost
non-overlapping occurrences of the pattern in string by the
replacement repl.  repl can be either a string or a callable;
if a string, backslash escapes in it are processed.  If it is
a callable, it's passed the match object and must return
a replacement string to be used.

Using this works in its place, however:

re.sub("(?i)mr", "", "Mr Bean")