Question

I have read the Google python regex tutorial about regular expression and tried to test one of the patterns I need.

• String must be 10 characters long.
• 1,3,5,7,9 chars must be digits (1 – 5) and should not be repeated
• other symbols are letters (a, b or c) and the can be repeated

For example:

1a2b4a3c5b # is valid

1a5c4b4a3b # is not valid because of two 4s

So far I’ve tried:

pattern = r'([1-5])[abc]([1-5^\1])[abc]([1-5^\1\2])[abc]([1-5\1\2\3])[abc]([1-5\1\2\3\4])[abc]'

but it failed…

Answer 1

I would suggest something like this instead of regex:

def matches(s):
    return (len(s) == 10 and 
            set(s[::2]) == set('12345') and 
            set(s[1::2]) <= set('abc'))

>>> matches('1a2b4a3c5b')
True
>>> matches('1a5c4b4a3b')
False