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Split up _determine_typevar_substitution
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@mrahtz
mrahtz committed Mar 5, 2022
1 parent 23b393b commit f094905
Showing 1 changed file with 106 additions and 76 deletions.
182 changes: 106 additions & 76 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1157,10 +1157,112 @@ def _is_unpacked_arbitrary_length_tuple(x: Any) -> bool:
_TypeVarOrTypeVarTuple = TypeVar | TypeVarTuple


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_substition_no_typevartuples(
typevars: tuple[TypeVar, ...],
args: tuple[type, ...]
) -> dict[TypeVar, type]:
if any(_is_unpacked_arbitrary_length_tuple(arg) for arg in args):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"unpacked arbitrary-length tuple to a TypeVar")
if len(typevars) != len(args):
raise TypeError(f"Number of type variables ({len(typevars)}) "
f"doesn't match number of type "
f"arguments ({len(args)})")
return dict(zip(typevars, args))


def _count_num_items_before_and_after(
items: tuple[Any, ...],
item_of_interest: Any,
) -> tuple[int, int]:
item_of_interest_idxs = [i for i, x in enumerate(items)
if x == item_of_interest]
if not item_of_interest_idxs:
raise ValueError("Item of interest not found")
if len(item_of_interest_idxs) > 1:
raise ValueError("Item of interest occurs more than once")
[item_of_interest_idx] = item_of_interest_idxs
num_start = item_of_interest_idx
# Assuming len(items) == 3:
# * If item_of_interest_idx == 0, there are 2 items after item_of_interest.
# * If item_of_interest_idx == 2, there are 0 items after item_of_interest.
num_end = len(items) - item_of_interest_idx - 1
return num_start, num_end


def _determine_typevar_substitution_single_typevartuple(
typevars: tuple[_TypeVarOrTypeVarTuple, ...],
args: tuple[type, ...]
) -> dict[_TypeVarOrTypeVarTuple, type | tuple[type, ...]]:
[typevartuple_idx] = [i for i, x in enumerate(typevars)
if isinstance(x, TypeVarTuple)]
typevartuple = typevars[typevartuple_idx]
num_start_typevars, num_end_typevars = _count_num_items_before_and_after(
typevars, typevartuple
)

# Even if one of the args is an unpacked arbitrary-length tuple, we still
# need at least as many args as normal TypeVars.
# Couldn't we split the arbitrary-length tuples across multiple TypeVars?
# No, because an arbitrary-length tuple could have length zero!
if len(args) < num_start_typevars + num_end_typevars:
raise TypeError(
"Expected at least {} type parameters, but only got {}".format(
num_start_typevars + num_end_typevars, len(args)
)
)

if num_start_typevars == num_end_typevars == 0:
# It's just a single TypeVarTuple.
return {typevars[0]: args}
elif num_end_typevars == 0:
args_for_typevartuple = args[num_start_typevars:]
args_for_typevars = args[:num_start_typevars]
if any(_is_unpacked_arbitrary_length_tuple(arg)
for arg in args_for_typevars):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"arbitrary-length tuple to a TypeVar")
return {
**dict(zip(typevars[:num_start_typevars], args_for_typevars)),
typevartuple: args_for_typevartuple,
}
else:
args_for_left_typevars = args[:num_start_typevars]
args_for_typevartuple = args[num_start_typevars:-num_end_typevars]
args_for_right_typevars = args[-num_end_typevars:]
if any(_is_unpacked_arbitrary_length_tuple(arg)
for arg in args_for_left_typevars + args_for_right_typevars):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"arbitrary-length tuple to a TypeVar")
return {
**dict(zip(typevars[:num_start_typevars], args_for_left_typevars)),
typevartuple: args_for_typevartuple,
**dict(zip(typevars[-num_end_typevars:], args_for_right_typevars)),
}


def _determine_typevar_substitution(
typevars: tuple[_TypeVarOrTypeVarTuple, ...],
args: tuple[type, ...]
) -> dict[_TypeVarOrTypeVarTuple, type]:
) -> dict[_TypeVarOrTypeVarTuple, type | tuple[type, ...]]:
"""Determines how to assign type arguments to type variables.
Args:
Expand Down Expand Up @@ -1256,83 +1358,11 @@ def _determine_typevar_substitution(
raise TypeError("At most 1 TypeVarTuple may be used in a type "
f"parameter list, but saw {num_typevartuples}")

# First, we should go through `args` to replace e.g. *tuple[int] with int.
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)
args = tuple(new_args)

# Case 1: typevars does not contain any TypeVarTuples
args = _replace_degenerate_unpacked_tuples(args)

if num_typevartuples == 0:
if any(_is_unpacked_arbitrary_length_tuple(arg) for arg in args):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"unpacked arbitrary-length tuple to a TypeVar")
if len(typevars) != len(args):
raise TypeError(f"Number of type variables ({len(typevars)}) "
f"doesn't match number of type "
f"arguments ({len(args)})")
return dict(zip(typevars, args))

# Case 2: typevars contains a single TypeVarTuple

[typevartuple_idx] = [i for i, x in enumerate(typevars)
if isinstance(x, TypeVarTuple)]
typevartuple = typevars[typevartuple_idx]
num_start_typevars = typevartuple_idx
# Assuming len(typevars) == 3:
# * If typevartuple_idx == 0, there are 2 TypeVars at
# the end of typevars.
# * If typevartuple_idx == 2 there are 0 TypeVars at
# the end of typevars.
num_end_typevars = len(typevars) - typevartuple_idx - 1

# Even if one of the args is an unpacked arbitrary-length tuple, we still
# need at least as many args as normal TypeVars.
# Couldn't we split the arbitrary-length tuples across multiple TypeVars?
# No, because an arbitrary-length tuple could have length zero!
if len(args) < num_start_typevars + num_end_typevars:
raise TypeError(
"Expected at least {} type parameters, but only got {}".format(
num_start_typevars + num_end_typevars, len(args)
)
)

if num_start_typevars == num_end_typevars == 0:
# It's just a single TypeVarTuple.
return {typevars[0]: args}
elif num_end_typevars == 0:
args_for_typevartuple = args[num_start_typevars:]
args_for_typevars = args[:num_start_typevars]
if any(_is_unpacked_arbitrary_length_tuple(arg)
for arg in args_for_typevars):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"arbitrary-length tuple to a TypeVar")
return {
**dict(zip(typevars[:num_start_typevars], args_for_typevars)),
typevartuple: args_for_typevartuple,
}
else:
args_for_left_typevars = args[:num_start_typevars]
args_for_typevartuple = args[num_start_typevars:-num_end_typevars]
args_for_right_typevars = args[-num_end_typevars:]
if any(_is_unpacked_arbitrary_length_tuple(arg)
for arg in args_for_left_typevars + args_for_right_typevars):
raise TypeError(f"Cannot assign type arguments '{args}' to type "
f"variables '{typevars}': cannot assign "
"arbitrary-length tuple to a TypeVar")
return {
**dict(zip(typevars[:num_start_typevars], args_for_left_typevars)),
typevartuple: args_for_typevartuple,
**dict(zip(typevars[-num_end_typevars:], args_for_right_typevars)),
}
return _determine_typevar_substition_no_typevartuples(typevars, args)
return _determine_typevar_substitution_single_typevartuple(typevars, args)


# Special typing constructs Union, Optional, Generic, Callable and Tuple
Expand Down

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