Allow unexpected values for ChoiceField/MultipleChoiceField representations

[shangxiao]

Closes #2839

[tomchristie]

I'd probably prefer to drop the indirection & just include this logic in the code as-is without the extra method.

[shangxiao]

That was actually my first attempt, although how would you inline a try/except inside a list comprehension? Was asking on #django and was told it may be possible with a generator expression & yielding?

[tomchristie]

Oh yup, I see that now. Missed the wrapping list comprehension.

[kevin-brown]

Can't you just do if six.text_type(value) in self.choice_strings_to_values instead of relying on a try/except here?

(Not suggesting that we remove the extra method, just commenting on the try/except that is being used)

[shangxiao]

Actually, perhaps a self.choice_strings_to_values.get(six.text_type(value), value) is better here?

[shangxiao]

@tomchristie an inline attempt: https://gist.github.com/rapilabs/93b983ea2313aa71137a

[tomchristie]

Method call is simpler afterall :)

[tomchristie]

Perfect!