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from typing import (
ChainMap,
TypeVar,
)
_KT = TypeVar("_KT")
_VT = TypeVar("_VT")
class DeepChainMap(ChainMap[_KT, _VT]):
"""
Variant of ChainMap that allows direct updates to inner scopes.
Only works when all passed mapping are mutable.
"""
def __setitem__(self, key: _KT, value: _VT) -> None:
for mapping in self.maps:
if key in mapping:
mapping[key] = value
return
self.maps[0][key] = value
def __delitem__(self, key: _KT) -> None:
"""
Raises
------
KeyError
If `key` doesn't exist.
"""
for mapping in self.maps:
if key in mapping:
del mapping[key]
return
raise KeyError(key)