I think pat1 = '[ab]' and pat2 = 'a|b' have the same function in Python(python2.7, windows) 're' module as a regular expression pattern. But I am confused with '[ab]+' and '(a|b)+', do they have the same function, if not plz explain details. ''' Created on 2012-9-4 @author: melo ''' import re pat1 = '(a|b)+' pat2 = '[ab]+' text = '22ababbbaa33aaa44b55bb66abaa77babab88' m1 = re.search(pat1, text) m2 = re.search(pat2, text) print 'search with pat1:', m1.group() print 'search with pat2:', m2.group() m11 = re.split(pat1, text) m22 = re.split(pat2, text) print 'split with pat1:', m11 print 'split with pat2:', m22 m111 = re.findall(pat1, text) m222 = re.findall(pat2, text) print 'findall with pat1:', m111 print 'findall with pat2:', m222 output as below: search with pat1: ababbbaa search with pat2: ababbbaa split with pat1: ['22', 'a', '33', 'a', '44', 'b', '55', 'b', '66', 'a', '77', 'b', '88'] split with pat2: ['22', '33', '44', '55', '66', '77', '88'] findall with pat1: ['a', 'a', 'b', 'b', 'a', 'b'] findall with pat2: ['ababbbaa', 'aaa', 'b', 'bb', 'abaa', 'babab'] why are 'pat1' and 'pat2' different and what's their difference? what kind of strings can 'pat1' actually match?