bpo-31581: Reduce the number of imports for functools #3757
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I added 'skip news' tag, since #1269 don't have news too. |
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The functools.singledispatch change seems reasonable to me, since the cost of checking the import cache twice will be cheap compared to the overhead of defining a new function to apply @singledispatch to.
As per the comments on the argparse PR, this should be accompanied by a comment explaining the trade-off (i.e. there are many programs that use functools without singledispatch, so we trade-off making singledispatch marginally slower for the benefit of making start-up of such applications slightly faster)
However, I'm less sure of the appropriateness of the start-up vs runtime cost trade-off for Counter.most_common, so I'd prefer to see that change in a separate PR.
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Lib/functools.py
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| # There are many programs that use functools without singledispatch, so we | ||
| # trade-off making singledispatch marginally slower for the benefit of | ||
| # making start-up of such applications slightly faster. | ||
| from types import MappingProxyType |
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It is slightly faster to import types and use types.MappingProxyType once than import MappingProxyType from types. The from ... import case runs a Python code from _bootstrap.py, while the former case runs just a C code if the types module already is imported.
Lib/test/test_functools.py
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| @@ -2033,9 +2035,9 @@ def __setitem__(self, key, value): | |||
| self.data[key] = value | |||
| def clear(self): | |||
| self.data.clear() | |||
| _orig_wkd = functools.WeakKeyDictionary | |||
| _orig_wkd = weakref.WeakKeyDictionary | |||
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Use try ... finally or test.support.swap_attr() for guaranteeing that weakref.WeakKeyDictionary is restored if the following checks fail.
fixed. |
Since functools and collections are very commonly used, it's worth enough to optimize import.
https://bugs.python.org/issue31581