(original) (raw)

In this case though, there are two pieces of information:

1\. A canonical key (which may or may not equal the original key);

2\. The original key.

It seems to me then that TransformDict is a specialised case of CanonicalDict, where the canonical key is defined to be the first key inserted. It would in fact be possible (though inefficient) to implement that using a canonicalising callable that maintained state - something like (untested):

class OriginalKeys:

def \_\_init\_\_(self)::

self.keys = CanonicalDict(str.lower)

def \_\_call\_\_(self, key):

return self.keys.setdefault(key, key)

class OriginalKeyDict(CanonicalDict):

def \_\_init\_\_(self)::

super().\_\_init\_\_(OriginalKeys())