Use flags_by key for faster access

[webjunkie]

No description provided.

[haacked]

The problem here is feature_flags_by_key is not guaranteed to be populated here.

[haacked]

Actually, I may be wrong. I think the problem is we have a lot of unit tests that only set self.client.feature_flags and do not set self.feature_flags_by_key.

[haacked]

I think a better solution would be to make feature_flags a @property. That way, we can pre-populate other related properties when it's set. Something like:

@property
    def feature_flags(self):
        return self._feature_flags

    @feature_flags.setter 
    def feature_flags(self, value):
        self._feature_flags = value
        self.feature_flags_by_key = {
            flag["key"]: flag for flag in (value or []) if flag.get("key") is not None
        }

That way, we won't need to update every unit test.