Lib/importlib/metadata/_context.py

from __future__ import annotations

import functools
import operator


# from jaraco.context 6.1
class ExceptionTrap:
    """
    A context manager that will catch certain exceptions and provide an
    indication they occurred.

    >>> with ExceptionTrap() as trap:
    ...     raise Exception()
    >>> bool(trap)
    True

    >>> with ExceptionTrap() as trap:
    ...     pass
    >>> bool(trap)
    False

    >>> with ExceptionTrap(ValueError) as trap:
    ...     raise ValueError("1 + 1 is not 3")
    >>> bool(trap)
    True
    >>> trap.value
    ValueError('1 + 1 is not 3')
    >>> trap.tb
    <traceback object at ...>

    >>> with ExceptionTrap(ValueError) as trap:
    ...     raise Exception()
    Traceback (most recent call last):
    ...
    Exception

    >>> bool(trap)
    False
    """

    exc_info = None, None, None

    def __init__(self, exceptions=(Exception,)):
        self.exceptions = exceptions

    def __enter__(self):
        return self

    @property
    def type(self):
        return self.exc_info[0]

    @property
    def value(self):
        return self.exc_info[1]

    @property
    def tb(self):
        return self.exc_info[2]

    def __exit__(self, *exc_info):
        type = exc_info[0]
        matches = type and issubclass(type, self.exceptions)
        if matches:
            self.exc_info = exc_info
        return matches

    def __bool__(self):
        return bool(self.type)

    def raises(self, func, *, _test=bool):
        """
        Wrap func and replace the result with the truth
        value of the trap (True if an exception occurred).

        First, give the decorator an alias to support Python 3.8
        Syntax.

        >>> raises = ExceptionTrap(ValueError).raises

        Now decorate a function that always fails.

        >>> @raises
        ... def fail():
        ...     raise ValueError('failed')
        >>> fail()
        True
        """

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            with ExceptionTrap(self.exceptions) as trap:
                func(*args, **kwargs)
            return _test(trap)

        return wrapper

    def passes(self, func):
        """
        Wrap func and replace the result with the truth
        value of the trap (True if no exception).

        First, give the decorator an alias to support Python 3.8
        Syntax.

        >>> passes = ExceptionTrap(ValueError).passes

        Now decorate a function that always fails.

        >>> @passes
        ... def fail():
        ...     raise ValueError('failed')

        >>> fail()
        False
        """
        return self.raises(func, _test=operator.not_)