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

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

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'))

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

    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.

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