On 2021-10-01 8:26 a.m., Steven D'Aprano wrote:
> I wish your proposals and ideas would be more *precise* in their
> specifications. This is not the first time that I have found it very
> hard to work out precisely what you are suggesting and what you are not.
>
>
Thanks for insisting on context managers. Does the attached context
manager clarify what the proposal is about?
# Antichecked Exceptions for Python
# Copyright (c) 2021 Soni L.
#
# Permission is hereby granted, free of charge, to any person ("You") obtaining
# a copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# This license shall be void if You bring a copyright lawsuit, related or
# unrelated to the Software, against any of the copyright holders.
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
class _hack:
def __init__(self, ctx):
self.ctx = ctx
def __enter__(self):
pass
def __exit__(self, exc_ty, exc_val, exc_tb):
exc_val.__context__ = self.ctx
class exceptions:
"""A context manager for antichecked exceptions.
Antichecked exceptions are the reverse of checked exceptions: rather than
requiring the caller to catch the exceptions, they actively check that
your function/block actually intended to raise them.
Examples:
>>> from antichecked import exceptions
Intercepting exceptions::
>>> with exceptions(StopIteration) as r:
... raise StopIteration
RuntimeError
Raising exceptions::
>>> with exceptions(StopIteration) as r:
... raise r(StopIteration)
StopIteration
Adding a cause::
>>> with exceptions(StopIteration) as r:
... raise r(StopIteration) from ValueError()
StopIteration from ValueError
Similarly, re-raising exceptions is done with ``raise r``.
"""
def __init__(self, *args):
"""Creates an antichecked exception context for the given exceptions.
Args:
Accepts an arbitrary amount of exception types.
"""
# each context manager gets an unique exception type
class WrappedError(Exception):
def __init__(self, exc=None):
if isinstance(exc, BaseException) or exc is None:
self.value = exc
else:
self.value = exc()
self._exceptions = args
self._error = WrappedError
def __enter__(self):
return self._error
def __exit__(self, exc_ty, exc_val, exc_tb):
if exc_ty is None:
return
if exc_ty is self._error:
# handle `raise r(exc)` similar to `raise exc`
if exc_val.value is not None:
exc = exc_val.value
exc.__cause__ = exc_val.__cause__
with _hack(exc_val.__context__):
raise exc.with_traceback(exc_tb)
# `raise r from foo` is unhandled, as `raise from foo` is not
# valid python. TODO make this case a RuntimeError.
pass
# handle `raise r` similar to `raise`
if exc_val.__context__ is None:
with _hack(None):
exc = RuntimeError("No active exception to re-raise")
raise exc.with_traceback(exc_tb)
with _hack(exc_val.__context__.__context__):
raise exc_val.__context__
if any(issubclass(exc_ty, e) for e in self._exceptions):
# handle this similar to StopIteration in generators
raise RuntimeError("Antichecked exception raised") from exc_val
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