The program takes a single string as a command line argument. It should print out the number of character classes contained in that string, e.g. for `aBN1`.

```
import sys

a = sys.argv[1]
if a.upper():  
    a = 1
elif a.lower():
    a = a + 1
elif a.digit():
    a = a + 1
else:
    a = a + 1

```

I use a for loop to include four character classes: digits, lower case characters, upper case characters and special characters, i.e. everything else.