How to correctly get all combinations of numbers in Python

Here is the code:

import itertoolsfor i in itertools.combinations_with_replacement('0123456789', 4):    print(''.join(i))

I need to get all combinations of digits by 4 with repetitions. Part of the program output:

00000001000200030004000500060007000800090011001200130014001500160017001800190022002300240025

Tell me, why after 0009 comes 0011, and not 0010? Also with 0022.