The following functions are involved in the implementation of regular expressions in Python:
1. re.findall() - This function accepts a pattern that is to be matched with the text string. It returns the strings that are a match.
2. re.sub() - Sub in “re.sub” stands for “substitution”. This method performs exactly the same function as the “re.findall()” function does.
3. re.split() - It separates the strings around the separator which is to be passed to it as its parameter. The separator could be anything.
4. re.search() - This function returns the match found in the string along with other string groups that it has captured.