[Python-Dev] PEP 455: TransformDict (original) (raw)

Serhiy Storchaka storchaka at gmail.com
Sat Oct 5 23:22:58 CEST 2013

06.10.13 00:08, Victor Stinner написав(ла):

2013/10/4 Raymond Hettinger <raymond.hettinger at gmail.com javascript:;>: > This contrasts with other tools like OrderedDict, ChainMap, > and namedtuple which started their lives outside the standard > library where we we able observe their fitness for real problems > being solved by real users.

Why do you say that TransformDict has no real use case, whereas similar containers are already used since many years in the Python standard library? Extract of the PEP: "Several modules in the standard library use identity lookups for object memoization, for example pickle, json, copy, cProfile, doctest and threadinglocal." I didn't check this whole list, but it looks like some modules can directly use TransformDict(id), see for example the copy module.

Unfortunately the pickle and the copy modules can't use TransformDict(id) because they expose their mappings (with integer id keys) in public API. At least until Python 4.0.

There are no so much use cases for IdentityDict in stdlib now, and even less for CaseInsensityDict. And a workaround is simple. I don't know about usage of TransformDict with other transfom function.

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