How to check if a string is a valid regex in Python?

Similar to Java. Use re.error exception:

import re

try:
    re.compile('[')
    is_valid = True
except re.error:
    is_valid = False

exception re.error

Exception raised when a string passed to one of the functions here is not a valid regular expression (for example, it might contain unmatched parentheses) or when some other error occurs during compilation or matching. It is never an error if a string contains no match for a pattern.

Another fancy way to write the same answer:

import re
try:
    print(bool(re.compile(input())))
except re.error:
    print('False')