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import sys
from pyramid.interfaces import (
IExceptionViewClassifier,
IRequest,
IView,
)
from zope.interface import providedBy
def excview_tween_factory(handler, registry):
""" A :term:`tween` factory which produces a tween that catches an
exception raised by downstream tweens (or the main Pyramid request
handler) and, if possible, converts it into a Response using an
:term:`exception view`."""
adapters = registry.adapters
def excview_tween(request):
attrs = request.__dict__
try:
response = handler(request)
except Exception as exc:
# WARNING: do not assign the result of sys.exc_info() to a local
# var here, doing so will cause a leak. We used to actually
# explicitly delete both "exception" and "exc_info" from ``attrs``
# in a ``finally:`` clause below, but now we do not because these
# attributes are useful to upstream tweens. This actually still
# apparently causes a reference cycle, but it is broken
# successfully by the garbage collector (see
# https://github.com/Pylons/pyramid/issues/1223).
attrs['exc_info'] = sys.exc_info()
attrs['exception'] = exc
# clear old generated request.response, if any; it may
# have been mutated by the view, and its state is not
# sane (e.g. caching headers)
if 'response' in attrs:
del attrs['response']
# we use .get instead of .__getitem__ below due to
# https://github.com/Pylons/pyramid/issues/700
request_iface = attrs.get('request_iface', IRequest)
provides = providedBy(exc)
for_ = (IExceptionViewClassifier, request_iface.combined, provides)
view_callable = adapters.lookup(for_, IView, default=None)
if view_callable is None:
raise
response = view_callable(exc, request)
return response
return excview_tween
MAIN = 'MAIN'
INGRESS = 'INGRESS'
EXCVIEW = 'pyramid.tweens.excview_tween_factory'
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