On May 31, 2010, at 7:31 PM, Benjamin Peterson wrote:
Lie Ryan <lie.1296@...> writes:
that their id() is expensive is implementation details, and the developer of PyPy should solve that instead of adding a clutch to the stdlib.
The stdlib isn't just about CPython. We already have optimized primitives for CPython, so I don't see why helping other implementations isn't a good cause.
Benjamin, could you elaborate of several points that are unclear: * If id() is expensive in PyPy, then how are they helped by the code in http://codespeak.net/svn/pypy/trunk/pypy/lib/identity_dict.py which uses id() for the gets and sets and contains? * In the examples you posted (such as http://codespeak.net/svn/pypy/trunk/pypy/tool/algo/graphlib.py ), it appears that PyPy already has an identity dict, so how are they helped by adding one to the collections module? * Most of the posted examples already work with regular dicts (which check identity before they check equality) -- don't the other implementations already implement regular dicts which need to have identity-implied-equality in order to pass the test suite? I would expect the following snippet to work under all versions and implementations of Python: >>> class A: ... pass >>> a = A() >>> d = {a: 10} >>> assert d[a] == 10 # uses a's identity for lookup * Is the proposal something needed for all implementations or is it just an optimization for a particular, non-CPython implementation? Raymond