Escaping regex string

Question

I want to use input from a user as a regex pattern for a search over some text. It works, but how I can handle cases where user puts characters that have meaning in regex?<

Answer 1

Unfortunately, re.escape() is not suited for the replacement string:

>>> re.sub('a', re.escape('_'), 'aa')
'\\_\\_'

A solution is to put the replacement in a lambda:

>>> re.sub('a', lambda _: '_', 'aa')
'__'

because the return value of the lambda is treated by re.sub() as a literal string.