Escaping regex string in Python

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? For example, the user wants to search for Word (s): regex engine will take the (s) as a group. I want it to treat it like a string "(s)". I can run replace on user input and replace the ( with \( and the ) with \) but the problem is I will need to do replace for every possible regex symbol. Do you know some better way ?

Answer

Use the re.escape() function for this:

4.2.3 re Module Contents

escape(string)

Return string with all non-alphanumerics backslashed; this is useful if you want to match an arbitrary literal string that may have regular expression metacharacters in it.

A simplistic example, search any occurence of the provided string optionally followed by 's', and return the match object.

def simplistic_plural(word, text):
    word_or_plural = re.escape(word) + 's?'
    return re.match(word_or_plural, text)