Check for certain set of characters

Check that a string contains only a certain
set of characters (in this case a-z, A-Z and 0-9).
import re

def is_allowed_specific_char(S):

    charRe = re.compile(r'[^a-zA-Z0-9.]')
    S = charRe.search(S)

    return not bool(S)

# test
print(is_allowed_specific_char("ABCDEFabcdef123450"))   # True
print(is_allowed_specific_char("*&%@#!}{"))             # False