Python string.replace regular expression

You are looking for the re.sub function.

import re
s = "Example String"
replaced = re.sub('[ES]', 'a', s)
print(replaced)

will print axample atring

str.replace() ^v2|v3 does not recognize regular expressions.

To perform a substitution using a regular expression, use re.sub() ^v2|v3.

For example:

import re

line = re.sub(
           r"(?i)^.*interfaceOpDataFile.*$", 
           "interfaceOpDataFile %s" % fileIn, 
           line
       )

In a loop, it would be better to compile the regular expression first:

import re

regex = re.compile(r"^.*interfaceOpDataFile.*$", re.IGNORECASE)
for line in some_file:
    line = regex.sub("interfaceOpDataFile %s" % fileIn, line)
    # do something with the updated line