Programming a cipher method using Python

[thatos]

I would like to make a code. If I have a letter 'a' must return 'c' and 'd' must return 'f' i.e. must convert each letter of a given word into the third letter from that letter.

[bartonc]

I would like to make a code. If I have a letter 'a' must return 'c' and 'd' must return 'f' i.e. must convert each letter of a given word into the third letter from that letter.

>>> cypher = dict(a='c', d='f')
>>> "".join([cypher[key] for key in list("ad")])
'cf'
>>>