How to exclude characters when counting digits

[gruntfutuk]

As you are dealing with a string, you can iterate through it with just:

for character in s:

character takes each character in turn in the loop.

As isdigit() returns True or False, you only need:

if character.isdigit():
    digit += 1

inside the loop.

For future information, you could replace it all with just a return line:

return sum(c.isdigit() for c in s)