import re  
def text_match(text):  
        patterns = 'ab??'  
        if re.search(patterns,  text):  
                return 'Found a match!'  
        else:  
                return('Not matched!')  
  
print(text_match("ab"))  
print(text_match("abc"))  
print(text_match("abbc"))  
print(text_match("aabbc"))  