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_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_)

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