Current File : //lib/python3/dist-packages/mypy/mro.py
from typing import Optional, Callable, List
from mypy.nodes import TypeInfo
from mypy.types import Instance
from mypy.typestate import TypeState
def calculate_mro(info: TypeInfo, obj_type: Optional[Callable[[], Instance]] = None) -> None:
"""Calculate and set mro (method resolution order).
Raise MroError if cannot determine mro.
"""
mro = linearize_hierarchy(info, obj_type)
assert mro, "Could not produce a MRO at all for %s" % (info,)
info.mro = mro
# The property of falling back to Any is inherited.
info.fallback_to_any = any(baseinfo.fallback_to_any for baseinfo in info.mro)
TypeState.reset_all_subtype_caches_for(info)
class MroError(Exception):
"""Raised if a consistent mro cannot be determined for a class."""
def linearize_hierarchy(info: TypeInfo,
obj_type: Optional[Callable[[], Instance]] = None) -> List[TypeInfo]:
# TODO describe
if info.mro:
return info.mro
bases = info.direct_base_classes()
if (not bases and info.fullname != 'builtins.object' and
obj_type is not None):
# Second pass in import cycle, add a dummy `object` base class,
# otherwise MRO calculation may spuriously fail.
# MRO will be re-calculated for real in the third pass.
bases = [obj_type().type]
lin_bases = []
for base in bases:
assert base is not None, "Cannot linearize bases for %s %s" % (info.fullname, bases)
lin_bases.append(linearize_hierarchy(base, obj_type))
lin_bases.append(bases)
return [info] + merge(lin_bases)
def merge(seqs: List[List[TypeInfo]]) -> List[TypeInfo]:
seqs = [s[:] for s in seqs]
result: List[TypeInfo] = []
while True:
seqs = [s for s in seqs if s]
if not seqs:
return result
for seq in seqs:
head = seq[0]
if not [s for s in seqs if head in s[1:]]:
break
else:
raise MroError()
result.append(head)
for s in seqs:
if s[0] is head:
del s[0]
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