How to get all the combinations of numbers in Python correctly

there is a code:

   IMPORT  ITERTOOLS  for  i  in  itertools.combinations_with_replacement ( '' 0123456789 ',  4 ):   print  ( '' ' .join (i))     
 I need to get all the combinations of 4 numbers with repetitions. Part of the output of the program: 
  
   0000  000100020003000500060007000800090011001200 130014001500160017001800190022002300240025    
 Tell me, tell me Why after  0009  there is  0011 , and not  0010 ? Also with  0022 .