[Python-Dev] Possible patch for functools partial (original) (raw)

Daniel Urban urban.dani at gmail.com
Thu May 13 11:51:23 CEST 2010

While a partial object should reasonably never change, you could change it:

from functools import partial p = partial(lambda *a, **kw: kw, 1, 2, spam='eggs') p() {'spam': 'eggs'} p.keywords['spam'] = 'bacon' p() {'spam': 'bacon'}

I realize touching p.keywords voids your warranty, but if we can stop people from doing it, maybe we should (or at least put a warning in the documentation, no?). So I'm thinking either we make an immutable/hashable dict while we're at it, or store the keyword arguments as a tuple (which guarantees immutability), and only convert them back to a dict when you want to call the partial object (simpler, slower).

You're right. I think it is possible to stop people from modifying p.keywords. If p.keywords wouldn't be a dict, but a read-only proxy for that dict, that may solve this problem. I think that is possible, with PyDictProxy_New [1]. But I'm not certain if that is a good idea, it may have side effects I'm not aware of. Any thoughts about this?

Your thoughts? Should we continue this discussion at issue8699? I don't know, I'm new here...

[1] http://docs.python.org/py3k/c-api/dict.html#PyDictProxy_New

Thanks, Daniel Urban

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