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 >>> 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_)