import sys
import re

try: #python 2
    _strtype = basestring
except NameError: #python 3
    _strtype = str

# Check equivalence of two regexes
# Each arg is either a str or a pair (str,flags)
def regex_eq(arg0,arg1):
    return re_debug(arg0) == re_debug(arg1)

#compile and catch the output
# Note: This clears the re module cache!
def re_debug(args):

    #break the args up into patterns and flags
    if isinstance(args,str): #if it's a string
        pattern = args
        flags = re.DEBUG
    else:
        pattern = args[0]
        flags = re.DEBUG | args[1] #else add to flag

    #save the real stdout, then compile with debug
    stdout = sys.stdout
    try:
        #to catch output of re.compile
        logger = writer()
        sys.stdout = logger

        #and compile
        re.purge() #a cache'd result
        re.compile(pattern,flags)
    finally:
        #uninstall the catcher
        sys.stdout = stdout
    return logger.log

class writer:
    #sys.stdout needs a write method
    def write(self,data):
        self.log += data
    def __init__(self):
        self.log = '';


### Example ###
re0 = "foo[bar]baz"
re1 = ("""foo   # foo!
          [bar] # b or a or r!
          baz   # baz!"""
       , re.VERBOSE)

regex_eq(re0,re1) #true
regex_eq('123','123*') #false
regex_eq('11*','1+') #true, returns false
regex_eq('(1)','1') #true, returns false
regex_eq('1?1*','1*') #true, returns false

'''
(Python 2 printing)

>>> print re_debug('11*')
literal 49
max_repeat 0 2147483647
  literal 49

>>> print re_debug('1+')
max_repeat 1 2147483647
  literal 49

>>> print re_debug('(1)')
subpattern 1
  literal 49
'''