command_context.py

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from contextlib import ExitStack, contextmanager
from typing import ContextManager, Generator, TypeVar
 
_T = TypeVar("_T", covariant=True)
 
 
class CommandContextMixIn:
    def __init__(self) -> None:
        super().__init__()
        self._in_main_context = False
        self._main_context = ExitStack()
 
    @contextmanager
    def main_context(self) -> Generator[None, None, None]:
        assert not self._in_main_context
 
        self._in_main_context = True
        try:
            with self._main_context:
                yield
        finally:
            self._in_main_context = False
 
    def enter_context(self, context_provider: ContextManager[_T]) -> _T:
        assert self._in_main_context
 
        return self._main_context.enter_context(context_provider)