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gh-102721: Improve coverage of _collections_abc._CallableGenericAlias #102722

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Mar 16, 2023
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gh-102721: Improve coverage of _collections_abc._CallableGenericAlias #102722

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gh-102721: Improve coverage of `_collections_abc._CallableGenericAlias`
sobolevn Mar 15, 2023
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sobolevn Mar 15, 2023
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7 changes: 0 additions & 7 deletions Lib/_collections_abc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -481,15 +481,8 @@ def __getitem__(self, item):
# rather than the default types.GenericAlias object. Most of the
# code is copied from typing's _GenericAlias and the builtin
# types.GenericAlias.

if not isinstance(item, tuple):
item = (item,)
# A special case in PEP 612 where if X = Callable[P, int],
# then X[int, str] == X[[int, str]].
if (len(self.__parameters__) == 1
and _is_param_expr(self.__parameters__[0])
and item and not _is_param_expr(item[0])):
item = (item,)
Comment on lines -487 to -492
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@AlexWaygood AlexWaygood Mar 15, 2023 •
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This makes me slightly nervous, but I can't find any changes in behaviour from removing this code.

@Fidget-Spinner and @serhiy-storchaka, can either of you think of anything bad that could happen if we remove this code? The whole test suite passes with it removed.

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Yes, me too. Let's wait for others to comment.

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It makes me nervous too. In case you're looking for an example that triggers this path, here's one:

from typing import ParamSpec
P = ParamSpec("P")
from collections.abc import Callable
C = Callable[[P], int]
print(C[str])

However I agree that if I just comment this out, the output is the same. It's possible that @serhiy-storchaka fixed the issue in the C code (the super() method) -- the code here is from Aug 4th, 2021, while he touched _Py_subs_parameters on May 8th, 2022.

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Yes, I found examples that triggered this code path, but for all of the examples I found, I couldn't find any differences in behaviour with this code deleted (repr, __args__, __parameters__, equality)

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Someone could trace through the C code that gets called and see if it does the right thing.

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Looks like _unpack_args C function which was added in May now handles this case: https://github.com/python/cpython/blame/2dc94634b50f0e5e207787e5ac1d56c68b22c3ae/Objects/genericaliasobject.c#L361

It unpacks nested tuples to a flat format, so - this code is not needed anymore.

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I don't suppose the pure-Python code could be useful for PyPy, could it? (Don't see how it could, just throwing that out there)

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Sorry, the only other iterperter I worked on is RustPython.


new_args = super().__getitem__(item).__args__

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39 changes: 32 additions & 7 deletions Lib/test/test_typing.py
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Expand Up @@ -1921,14 +1921,29 @@ def test_weakref(self):
self.assertEqual(weakref.ref(alias)(), alias)

def test_pickle(self):
global T_pickle, P_pickle, TS_pickle # needed for pickling
Callable = self.Callable
alias = Callable[[int, str], float]
for proto in range(pickle.HIGHEST_PROTOCOL + 1):
s = pickle.dumps(alias, proto)
loaded = pickle.loads(s)
self.assertEqual(alias.__origin__, loaded.__origin__)
self.assertEqual(alias.__args__, loaded.__args__)
self.assertEqual(alias.__parameters__, loaded.__parameters__)
T_pickle = TypeVar('T_pickle')
P_pickle = ParamSpec('P_pickle')
TS_pickle = TypeVarTuple('TS_pickle')

samples = [
Callable[[int, str], float],
Callable[P_pickle, int],
Callable[P_pickle, T_pickle],
Callable[Concatenate[int, P_pickle], int],
Callable[Concatenate[*TS_pickle, P_pickle], int],
]
for alias in samples:
for proto in range(pickle.HIGHEST_PROTOCOL + 1):
with self.subTest(alias=alias, proto=proto):
s = pickle.dumps(alias, proto)
loaded = pickle.loads(s)
self.assertEqual(alias.__origin__, loaded.__origin__)
self.assertEqual(alias.__args__, loaded.__args__)
self.assertEqual(alias.__parameters__, loaded.__parameters__)

del T_pickle, P_pickle, TS_pickle # cleaning up global state

def test_var_substitution(self):
Callable = self.Callable
Expand All @@ -1954,6 +1969,16 @@ def test_var_substitution(self):
self.assertEqual(C5[int, str, float],
Callable[[typing.List[int], tuple[str, int], float], int])

def test_type_subst_error(self):
Callable = self.Callable
P = ParamSpec('P')
T = TypeVar('T')

pat = "Expected a list of types, an ellipsis, ParamSpec, or Concatenate."

with self.assertRaisesRegex(TypeError, pat):
Callable[P, T][0, int]

def test_type_erasure(self):
Callable = self.Callable
class C1(Callable):
Expand Down