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from __future__ import annotations
from typing import TYPE_CHECKING
if TYPE_CHECKING:
from returns.interfaces.unwrappable import Unwrappable # noqa: WPS433
class UnwrapFailedError(Exception):
"""Raised when a container can not be unwrapped into a meaningful value."""
__slots__ = ('halted_container',)
def __init__(self, container: Unwrappable) -> None:
"""
Saves halted container in the inner state.
So, this container can later be unpacked from this exception
and used as a regular value.
"""
super().__init__()
self.halted_container = container
def __reduce__(self): # noqa: WPS603
"""Custom reduce method for pickle protocol.
This helps properly reconstruct the exception during unpickling.
"""
return (
self.__class__, # callable
(self.halted_container,), # args to callable
)
class ImmutableStateError(AttributeError):
"""
Raised when a container is forced to be mutated.
It is a sublclass of ``AttributeError`` for two reasons:
1. It seems kinda reasonable to expect ``AttributeError``
on attribute modification
2. It is used inside ``typing.py`` this way,
we do have several typing features that requires that behaviour
See: https://github.com/dry-python/returns/issues/394
"""
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