New submission from Dan Snider <[email protected]>:
The title was carefully worded as I have no idea how or why what is happening
is happening, only that it has been like this since a least 3.6.0. That version
in particular, by the way, is able to execute a call to a python function with
1 argument 25% faster than 3.8.0 but that may be due at least in part by
whatever it is that makes it much faster to a call a unary function wrapped by
functools.partial by utilizing the subcript operator on an instance of a
partial subtype whose __getitem__ has been set to the data descriptor
partial.func... Eg:
class Party(partial): __getitem__ = partial.func
fast = Party(hash)
slow = partial(hash)
# the expression `fast[""]` runs approximately 28% faster than
# the expression `slow("")`, and partial.func as __getitem__ is
# confusingly 139% faster than partial.__call__...
That rather large digression aside, here's a demonstration of two functions
identical in every way except the CO_NESTED bit and perhaps the names:
if 1:
def Slow():
global Slow
class Slow:
global slow
def slow(self): return self
return Slow
if Slow():
class Fast:
global fast
def fast(self): return self
import dis
dis.show_code(slow)
print()
dis.show_code(fast)
----------
messages: 359700
nosy: bup
priority: normal
severity: normal
status: open
title: The CO_NESTED flag is associated with a significant performance cost
type: performance
versions: Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue39281>
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