Performance of attribute lookup for type objects

[eendebakpt]

Bug report

The performance of attribute lookup for type objects is worse than for other objects. A benchmark

import pyperf
runner=pyperf.Runner()

setup="""
class Class:
    def all(self):
        pass

x=Class()
"""

runner.timeit('hasattr x.all', "hasattr(x, 'all')", setup=setup)
runner.timeit('hasattr x.__array_ufunc__', "hasattr(x, '__array_ufunc__')", setup=setup)
runner.timeit('hasattr Class.all', "hasattr(Class, 'all')", setup=setup)
runner.timeit('hasattr Class.__array_ufunc__', "hasattr(Class, '__array_ufunc__')", setup=setup) # worse performance

Results:

hasattr x.all: Mean +- std dev: 68.1 ns +- 1.1 ns
hasattr x.__array_ufunc__: Mean +- std dev: 40.4 ns +- 0.3 ns
hasattr Class.all: Mean +- std dev: 38.1 ns +- 0.6 ns
hasattr Class.__array_ufunc__: Mean +- std dev: 255 ns +- 2 ns

The reason seems to be that the type_getattro always executes PyErr_Format, wheras for the "normal" attribute lookup this is avoided (see here and here)

Notes:

• The benchmark is from the python side, but we are working with the C-API
• The performance is important for numpy, see PERF: Improve performance of special attribute lookups numpy/numpy#21423
• Another location where this is a bottleneck: https://github.com/python/cpython/blob/v3.12.0a2/Lib/dataclasses.py#L1301

Your environment

• CPython versions tested on: Python 3.11.0a7+
• Operating system and architecture: Linux Ubuntu

Linked PRs

• gh-92216: improve performance of hasattr for type objects #99977
• gh-92216: improve performance of hasattr for type objects #99979

[seberg]

Related to this issue, I am wondering if we can consider _PyObject_LookupAttr either as stable (removing the _) or as "semi stable"?
Of course that is only faster currently for the default tp_getattro, but I suspect that is a huge amount of calls.

EDIT: Ah, I half thought it was not fully internal API right now, but "semi" exposed.

[eendebakpt]

Also see: #76752 (PRs where _PyObject_LookupAttr is introduced)

[serhiy-storchaka]

_PyObject_LookupAttr is an internal API.

I'll look if it is possible to speed up lookup of the absent attribute in a class object.

[Fidget-Spinner]

@eendebakpt thanks for the improvement. Can I close this issue now or do you plan to submit more PRs?

[eendebakpt]

The issue is solved, i will close