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bpo-43224: Add more tests for typevar substitution #31844

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eb1a7ab
Refactor typevar substitution into separate helper for easier testing
mrahtz Mar 13, 2022
f500d59
Deal properly with e.g. *tuple[int]
mrahtz Mar 13, 2022
8611053
Add more tests for typevar substitution
mrahtz Mar 13, 2022
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120 changes: 120 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@
from typing import TypeAlias
from typing import ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs
from typing import TypeGuard
from typing import _determine_typevar_substitution
import abc
import textwrap
import typing
Expand Down Expand Up @@ -843,6 +844,125 @@ class C(Generic[Unpack[Ts]]): pass
self.assertNotEqual(C[Unpack[Ts1]], C[Unpack[Ts2]])


class TypeVarSubstitutionTests(BaseTestCase):

def test_valid_substitution(self):
T1 = TypeVar('T1')
T2 = TypeVar('T2')
Ts = TypeVarTuple('Ts')

# These are tuples of (typevars, args, expected_result).
test_cases = [
# TypeVars only
((T1,), (int,), {T1: int}),
((T1,), (tuple[int, ...],), {T1: tuple[int, ...]}),
((T1,), (Unpack[tuple[int]],), {T1: int}),
((T1, T2), (int, str), {T1: int, T2: str}),
((T1, T2), (tuple[int, ...], tuple[str, ...]), {T1: tuple[int, ...], T2: tuple[str, ...]}),
((T1, T2), (Unpack[tuple[int, str]],), {T1: int, T2: str}),
# TypeVarTuple only
((Ts,), (), {Ts: ()}),
((Ts,), (int,), {Ts: (int,)}),
((Ts,), (tuple[int, ...],), {Ts: (tuple[int, ...],)}),
((Ts,), (Unpack[tuple[int]],), {Ts: (int,)}),
((Ts,), (int, str), {Ts: (int, str)}),
((Ts,), (tuple[int, ...], tuple[str, ...]), {Ts: (tuple[int, ...], tuple[str, ...])}),
((Ts,), (Unpack[tuple[int, ...]],), {Ts: (Unpack[tuple[int, ...]],)}),
# TypeVarTuple at the beginning
((Ts, T1), (int,), {Ts: (), T1: int}),
((Ts, T1), (tuple[int, ...],), {Ts: (), T1: tuple[int, ...]}),
((Ts, T1), (int, str), {Ts: (int,), T1: str}),
((Ts, T1), (int, str, float), {Ts: (int, str), T1: float}),
((Ts, T1), (Unpack[tuple[int, ...]], str), {Ts: (Unpack[tuple[int, ...]],), T1: str}),
((Ts, T1), (Unpack[tuple[int, ...]], str, bool), {Ts: (Unpack[tuple[int, ...]], str), T1: bool}),
# TypeVarTuple at the end
((T1, Ts), (int,), {T1: int, Ts: ()}),
((T1, Ts), (int, str), {T1: int, Ts: (str,)}),
((T1, Ts), (int, str, float), {T1: int, Ts: (str, float)}),
((T1, Ts), (int, Unpack[tuple[str, ...]]), {T1: int, Ts: (Unpack[tuple[str, ...]],)}),
((T1, Ts), (int, str, Unpack[tuple[float, ...]]), {T1: int, Ts: (str, Unpack[tuple[float, ...]],)}),
# TypeVarTuple in the middle
((T1, Ts, T2), (int, str), {T1: int, Ts: (), T2: str}),
((T1, Ts, T2), (int, float, str), {T1: int, Ts: (float,), T2: str}),
((T1, Ts, T2), (int, Unpack[tuple[int, ...]], str), {T1: int, Ts: (Unpack[tuple[int, ...]],), T2: str}),
((T1, Ts, T2), (int, float, Unpack[tuple[bool, ...]], str), {T1: int, Ts: (float, Unpack[tuple[bool, ...]],), T2: str}),
((T1, Ts, T2), (int, Unpack[tuple[bool, ...]], float, str), {T1: int, Ts: (Unpack[tuple[bool, ...]], float), T2: str}),
((T1, Ts, T2), (int, complex, Unpack[tuple[bool, ...]], float, str), {T1: int, Ts: (complex, Unpack[tuple[bool, ...]], float), T2: str})
]
for typevars, args, expected_result in test_cases:
with self.subTest(f'typevars={typevars}, args={args}'):
self.assertEqual(
expected_result,
_determine_typevar_substitution(
cls=None, params=typevars, args=args
)
)

def test_too_few_args_raises_exception(self):
T1 = TypeVar('T1')
T2 = TypeVar('T2')

# We don't include test cases including TypeVarTuples because we
# decided not to implement arity checking of variadic generics
# in order to reduce complexity.
test_cases = [
# One TypeVar: invalid if 0 args
((T1,), ()),
((T1,), (Unpack[tuple[()]],)),
# Two TypeVars: invalid if <= 1 args
((T1, T2), (int,)),
((T1, T2), (Unpack[tuple[int]],)),
]
for typevars, args in test_cases:
with self.subTest(f'typevars={typevars}, args={args}'):
with self.assertRaises(TypeError):
_determine_typevar_substitution(
cls=None, params=typevars, args=args
)

def test_too_many_args_raises_exception(self):
T1 = TypeVar('T1')
T2 = TypeVar('T2')

# We don't include test cases including TypeVarTuples because we
# decided not to implement arity checking of variadic generics
# in order to reduce complexity.
test_cases = [
# One TypeVar: invalid if >= 2 args
((T1,), (int, int)),
((T1,), (Unpack[tuple[int, int]],)),
((T1,), (Unpack[tuple[int]], Unpack[tuple[int]])),
# Two TypeVars: invalid if >= 3 args
((T1, T2), (int, int, int)),
((T1, T2), (Unpack[tuple[int, int, int]],)),
((T1, T2), (Unpack[tuple[int]], Unpack[tuple[int]], Unpack[tuple[int]])),
]

for typevars, args in test_cases:
with self.subTest(f'typevars={typevars}, args={args}'):
with self.assertRaises(TypeError):
_determine_typevar_substitution(
cls=None, params=typevars, args=args
)

def test_too_many_typevartuples_raises_exception(self):
T = TypeVar('T')
Ts = TypeVarTuple('Ts')

test_cases = [
((T, Ts, Ts), (int, str)),
((Ts, T, Ts), (int, str)),
((Ts, Ts, T), (int, str))
]

for typevars, args in test_cases:
with self.subTest(f'typevars={typevars}, args={args}'):
with self.assertRaises(TypeError):
_determine_typevar_substitution(
cls=None, params=typevars, args=args
)


class UnionTests(BaseTestCase):

def test_basics(self):
Expand Down
56 changes: 39 additions & 17 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1269,11 +1269,6 @@ def __getitem__(self, args):
if (self._paramspec_tvars
and any(isinstance(t, ParamSpec) for t in self.__parameters__)):
args = _prepare_paramspec_params(self, args)
elif not any(isinstance(p, TypeVarTuple) for p in self.__parameters__):
# We only run this if there are no TypeVarTuples, because we
# don't check variadic generic arity at runtime (to reduce
# complexity of typing.py).
_check_generic(self, args, len(self.__parameters__))

new_args = self._determine_new_args(args)
r = self.copy_with(new_args)
Expand All @@ -1296,18 +1291,7 @@ def _determine_new_args(self, args):

params = self.__parameters__
# In the example above, this would be {T3: str}
new_arg_by_param = {}
for i, param in enumerate(params):
if isinstance(param, TypeVarTuple):
j = len(args) - (len(params) - i - 1)
if j < i:
raise TypeError(f"Too few arguments for {self}")
new_arg_by_param.update(zip(params[:i], args[:i]))
new_arg_by_param[param] = args[i: j]
new_arg_by_param.update(zip(params[i + 1:], args[j:]))
break
else:
new_arg_by_param.update(zip(params, args))
new_arg_by_param = _determine_typevar_substitution(self, params, args)

new_args = []
for old_arg in self.__args__:
Expand Down Expand Up @@ -1401,6 +1385,44 @@ def __iter__(self):
yield Unpack[self]


def _replace_degenerate_unpacked_tuples(
args: tuple[type, ...]
) -> tuple[type, ...]:
"""Replaces e.g. `*tuple[int]` with just `int` in `args`."""
new_args = []
for arg in args:
if (_is_unpacked_tuple(arg)
and not _is_unpacked_arbitrary_length_tuple(arg)):
arg_tuple = arg.__args__[0] # The actual tuple[int]
new_args.extend(arg_tuple.__args__)
else:
new_args.append(arg)
return tuple(new_args)


def _determine_typevar_substitution(cls, params, args):
args = _replace_degenerate_unpacked_tuples(args)
new_arg_by_param = {}
for i, param in enumerate(params):
if isinstance(param, TypeVarTuple):
j = len(args) - (len(params) - i - 1)
if j < i:
raise TypeError("Too few type arguments")
new_arg_by_param.update(zip(params[:i], args[:i]))
new_arg_by_param[param] = args[i: j]
new_arg_by_param.update(zip(params[i + 1:], args[j:]))
if any(isinstance(param, TypeVarTuple) for param in params[i + 1:]):
raise TypeError("Only one TypeVarTuple may be used in type parameters")
break
else:
# We only run this if there are no TypeVarTuples, because we
# don't check variadic generic arity at runtime (to reduce
# complexity of typing.py).
_check_generic(cls, args, len(params))
new_arg_by_param.update(zip(params, args))
return new_arg_by_param


# _nparams is the number of accepted parameters, e.g. 0 for Hashable,
# 1 for List and 2 for Dict. It may be -1 if variable number of
# parameters are accepted (needs custom __getitem__).
Expand Down