Bob is a lazy man. 
He needs you to create a method that can determine how many ```letters``` and ```digits``` are in a given string.
Example:
"hel2!lo" --> 6
"wicked .. !" --> 6
"!?..A" --> 1
import re
def count_letters_and_digits(s):
    if s == None or s == []:
        return 0
    return len(re.findall("[A-Za-z0-9]",s))
import re
def count_letters_and_digits(s):
    if s == None or s == []:
        return 0
    return len(re.findall("[A-Za-z0-9]",s))