Why doesn't str.translate work in Python 3?

Question

Why does \'a\'.translate({\'a\':\'b\'}) return \'a\' instead of \'b\'? I\'m using Python 3.

Answer 1

The keys used are the ordinals of the characters, not the characters themselves:

'a'.translate({ord('a'): 'b'})

It's easier to use str.maketrans

>>> 'a'.translate(str.maketrans('a', 'b'))
'b'

>>> help(str.translate)
Help on method_descriptor:

translate(...)
    S.translate(table) -> str

    Return a copy of the string S, where all characters have been mapped
    through the given translation table, which must be a mapping of
    Unicode ordinals to Unicode ordinals, strings, or None.
    Unmapped characters are left untouched. Characters mapped to None
    are deleted.