Replace generic string with something else in python

Question

I basically have strings that might be like this

str1 = "Z (X) Z"
str2 = "Z .X. Z"
str3 = "Z 'X' Z"

The X might be anything, as well as Z: for example:

str1 = "(example1)         "
str2 = "random_stuff .example2. other_random_stuff"
str3 = "'example3' stuff"

What I need is to replace the X with something else, but how can I do that if the X could be anything? I have to extrapolate the portion of string delimited by "..", "()", "''" (the X portion) and replace it with something else. Z portions can be anything as well and they should not be considered, and the X thing can be found in the middle of the string as well so i cant use this:

str1 = ".X."
str_to_be_changed = str1[1][-1]
str1.replace(str_to_be_changed, "Y")

Thanks :)

Answer 1

You'd use a regular expression with a replacement function:

import re

def change_string(string, replacement):
    def repl(match):
        o, c = match.group('open'), match.group('close')
        if o + c in ('..', "''", '()'):
            return '{}{}{}'.format(o, replacement, c)
        return match.group(0)
    return re.sub(r"(?P<open>['.(]).*?(?P<close>['.)])", repl, string)

The repl() function verifies that the opener and closing characters match up before replacing.

Demo:

>>> str1 = ".X."
>>> change_string(str1, 'Y')
'.Y.'
>>> change_string("This is a larger 'example' with (more than one) replacement, including a 'false positive.", 'Y')
"This is a larger 'Y' with (Y) replacement, including a 'false positive."

Answer 2

Try using str.format()

For example:

l = ".{}."
print l.format("mything")
'.mything.'