I want to decrypt a string by incrementing each letter by two alpha positions *i.e.* 'a' becomes 'c'. I've used `chr` and `ord` for the increments but can't work out how to skip over the special characters in the string such as spaces and parenthesis. 

```
from sys import stdout
from time import sleep

encodedString = 'g fmnc wms'

stringLength = len(encodedString)

for i in range(0, stringLength):
    if encodedString[i].isalpha():
        decodedString = chr(ord(encodedString[i]) + 2)
        stdout.write("\r%s" % decodedString)
        stdout.flush()
        sleep(0.1)
stdout.write("\n")

```