gh-144191: Dataclasses single field ordering #144222
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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
johnslavik
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Thanks! You can wait for the green light from Eric before going forward or add tests for this even now. I'd probably change test_1_field_compare. And of course a news entry, too.
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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
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Hey @picnixz and @johnslavik, just a quick update: I ran a small local benchmark on a CPython 3.15 dev build to ensure this change doesn't cause any noticeable slowdown. In my tests, the I’m happy to follow your advice on this. If you’d rather test it yourselves or revert to the |
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Just for reference, here are the numbers I observed locally (CPython 3.15 dev build):
These were consistent across repeated runs. |
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Please share the benchmarking script and the way you ran it. Class creation matters when considering import time as well. |
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The script was executed using the freshly built interpreter. Each implementation ( Scriptimport timeit
import sys
from dataclasses import dataclass
class MockField:
def __init__(self, name):
self.name = name
def _tuple_str(obj_name, flds):
if not flds:
return '()'
return f'({",".join(f"{obj_name}.{f.name}" for f in flds)},)'
def match_impl(flds):
match flds:
case [single_fld]:
self_expr = f"self.{single_fld.name}"
other_expr = f"other.{single_fld.name}"
case _:
self_expr = _tuple_str("self", flds)
other_expr = _tuple_str("other", flds)
return self_expr, other_expr
def ifelse_impl(flds):
if len(flds) == 1:
self_expr = f"self.{flds[0].name}"
other_expr = f"other.{flds[0].name}"
else:
self_expr = _tuple_str("self", flds)
other_expr = _tuple_str("other", flds)
return self_expr, other_expr
def run_benchmark():
single_field = [MockField("value")]
multi_field = [MockField("x"), MockField("y"), MockField("z")]
iterations = 1_000_000
# Just to make sure that I am using the local build
print("Python:", sys.version)
print("Executable:", sys.executable)
print()
print("Single-field case")
print("match/case:", timeit.timeit(lambda: match_impl(single_field), number=iterations))
print("if/else:", timeit.timeit(lambda: ifelse_impl(single_field), number=iterations))
print("Multi-field case")
print("match/case:", timeit.timeit(lambda: match_impl(multi_field), number=iterations))
print("if/else:", timeit.timeit(lambda: ifelse_impl(multi_field), number=iterations))
print("Real dataclass comparison (sanity check)")
@dataclass(order=True)
class A:
x: int
@dataclass(order=True)
class B:
x: int
y: int
z: int
a1, a2 = A(1), A(2)
b1, b2 = B(1, 2, 3), B(2, 3, 4)
print("single-field:", timeit.timeit(lambda: a1 < a2, number=iterations))
print("multi-field: ", timeit.timeit(lambda: b1 < b2, number=iterations))
if __name__ == "__main__":
run_benchmark() |
Simplify single-field dataclass ordering comparisons
#144191