Source code for mode.utils.contexts

"""Context manager utilities."""
from types import TracebackType
from typing import Any, Optional, Type

try:  # pragma: no cover
    from contextlib import AbstractAsyncContextManager
    from contextlib import AsyncExitStack, ExitStack
    from contextlib import asynccontextmanager
    from contextlib import nullcontext
except ImportError:  # pragma: no cover
    from ._py37_contextlib import AbstractAsyncContextManager
    from ._py37_contextlib import AsyncExitStack, ExitStack
    from ._py37_contextlib import asynccontextmanager
    from ._py37_contextlib import nullcontext

__all__ = [
    'AbstractAsyncContextManager',
    'AsyncExitStack',
    'ExitStack',
    'asynccontextmanager',
    'nullcontext',
    'asyncnullcontext',
]


# Sphinx complains that stdlib is badly formatted :P

AsyncExitStack.__doc__ = '''
Async context manager for dynamic management of a stack of exit
callbacks.

Example:
    >>> async with AsyncExitStack() as stack:
    ...    connections = [await stack.enter_async_context(get_connection())
    ...                   for i in range(5)]
    ...    # All opened connections will automatically be released at the
    ...    # end of the async with statement, even if attempts to open a
    ...    # connection later in the list raise an exception.
'''
asynccontextmanager.__doc__ = 'asynccontextmanager decorator.'
nullcontext.__doc__ = 'Context that does nothing.'


class asyncnullcontext(AbstractAsyncContextManager):
    """Context for async-with statement doing nothing."""

    enter_result: Any

    def __init__(self, enter_result: Any = None) -> None:
        self.enter_result = enter_result

    async def __aenter__(self) -> 'asyncnullcontext':
        return self.enter_result

    async def __aexit__(self,
                        exc_type: Type[BaseException] = None,
                        exc_val: BaseException = None,
                        exc_tb: TracebackType = None) -> Optional[bool]:
        ...