Match ‘a’ followed by zero or one char

pattern = ‘a?’

Write a python program that matches a string
that has an a followed by zero or one ‘b’.
import re

def text_match(S):

    pattern = 'a?'

    if re.search(pattern,  S):
        return 'Found a match!'
    else:
        return('Not matched!')

# test
print(text_match("ab"))     # Found a match!
print(text_match("abc"))    # Found a match!
print(text_match("abbc"))   # Found a match!
print(text_match("aabbc"))  # Found a match!