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Optimize subtype checking by avoiding a nested function #14325

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Dec 20, 2022
Merged

Optimize subtype checking by avoiding a nested function #14325

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31 changes: 20 additions & 11 deletions mypy/subtypes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -289,18 +289,20 @@ def _is_subtype(
# ErasedType as we do for non-proper subtyping.
return True

def check_item(left: Type, right: Type, subtype_context: SubtypeContext) -> bool:
if proper_subtype:
return is_proper_subtype(left, right, subtype_context=subtype_context)
return is_subtype(left, right, subtype_context=subtype_context)

if isinstance(right, UnionType) and not isinstance(left, UnionType):
# Normally, when 'left' is not itself a union, the only way
# 'left' can be a subtype of the union 'right' is if it is a
# subtype of one of the items making up the union.
is_subtype_of_item = any(
check_item(orig_left, item, subtype_context) for item in right.items
)
if proper_subtype:
is_subtype_of_item = any(
is_proper_subtype(orig_left, item, subtype_context=subtype_context)
for item in right.items
)
else:
is_subtype_of_item = any(
is_subtype(orig_left, item, subtype_context=subtype_context)
for item in right.items
)
# Recombine rhs literal types, to make an enum type a subtype
# of a union of all enum items as literal types. Only do it if
# the previous check didn't succeed, since recombining can be
Expand All @@ -312,9 +314,16 @@ def check_item(left: Type, right: Type, subtype_context: SubtypeContext) -> bool
and (left.type.is_enum or left.type.fullname == "builtins.bool")
):
right = UnionType(mypy.typeops.try_contracting_literals_in_union(right.items))
is_subtype_of_item = any(
check_item(orig_left, item, subtype_context) for item in right.items
)
if proper_subtype:
is_subtype_of_item = any(
is_proper_subtype(orig_left, item, subtype_context=subtype_context)
for item in right.items
)
else:
is_subtype_of_item = any(
is_subtype(orig_left, item, subtype_context=subtype_context)
for item in right.items
)
# However, if 'left' is a type variable T, T might also have
# an upper bound which is itself a union. This case will be
# handled below by the SubtypeVisitor. We have to check both
Expand Down