Current File : //lib/python3/dist-packages/mypy/solve.py
"""Type inference constraint solving"""
from typing import List, Dict, Optional
from collections import defaultdict
from mypy.types import Type, AnyType, UninhabitedType, TypeVarId, TypeOfAny, get_proper_type
from mypy.constraints import Constraint, SUPERTYPE_OF
from mypy.join import join_types
from mypy.meet import meet_types
from mypy.subtypes import is_subtype
def solve_constraints(vars: List[TypeVarId], constraints: List[Constraint],
strict: bool = True) -> List[Optional[Type]]:
"""Solve type constraints.
Return the best type(s) for type variables; each type can be None if the value of the variable
could not be solved.
If a variable has no constraints, if strict=True then arbitrarily
pick NoneType as the value of the type variable. If strict=False,
pick AnyType.
"""
# Collect a list of constraints for each type variable.
cmap: Dict[TypeVarId, List[Constraint]] = defaultdict(list)
for con in constraints:
cmap[con.type_var].append(con)
res: List[Optional[Type]] = []
# Solve each type variable separately.
for tvar in vars:
bottom: Optional[Type] = None
top: Optional[Type] = None
candidate: Optional[Type] = None
# Process each constraint separately, and calculate the lower and upper
# bounds based on constraints. Note that we assume that the constraint
# targets do not have constraint references.
for c in cmap.get(tvar, []):
if c.op == SUPERTYPE_OF:
if bottom is None:
bottom = c.target
else:
bottom = join_types(bottom, c.target)
else:
if top is None:
top = c.target
else:
top = meet_types(top, c.target)
top = get_proper_type(top)
bottom = get_proper_type(bottom)
if isinstance(top, AnyType) or isinstance(bottom, AnyType):
source_any = top if isinstance(top, AnyType) else bottom
assert isinstance(source_any, AnyType)
res.append(AnyType(TypeOfAny.from_another_any, source_any=source_any))
continue
elif bottom is None:
if top:
candidate = top
else:
# No constraints for type variable -- 'UninhabitedType' is the most specific type.
if strict:
candidate = UninhabitedType()
candidate.ambiguous = True
else:
candidate = AnyType(TypeOfAny.special_form)
elif top is None:
candidate = bottom
elif is_subtype(bottom, top):
candidate = bottom
else:
candidate = None
res.append(candidate)
return res
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