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# -*- coding: utf-8 -*-
Utilities for safely pickling exceptions.
:copyright: (c) 2009 - 2012 by Ask Solem.
:license: BSD, see LICENSE for more details.
from __future__ import absolute_import
import inspect
import sys
import types
from copy import deepcopy
import pickle as pypickle
import cPickle as cpickle
except ImportError:
cpickle = None # noqa
from .encoding import safe_repr
if sys.version_info < (2, 6): # pragma: no cover
# cPickle is broken in Python <= 2.6.
# It unsafely and incorrectly uses relative instead of absolute imports,
# so e.g.:
# exceptions.KeyError
# becomes:
# celery.exceptions.KeyError
# Your best choice is to upgrade to Python 2.6,
# as while the pure pickle version has worse performance,
# it is the only safe option for older Python versions.
pickle = pypickle
pickle = cpickle or pypickle
#: List of base classes we probably don't want to reduce to.
unwanted_base_classes = (StandardError, Exception, BaseException, object)
if sys.version_info < (2, 5): # pragma: no cover
# Prior to Python 2.5, Exception was an old-style class
def subclass_exception(name, parent, unused):
return types.ClassType(name, (parent,), {})
def subclass_exception(name, parent, module): # noqa
return type(name, (parent,), {'__module__': module})
def find_nearest_pickleable_exception(exc):
"""With an exception instance, iterate over its super classes (by mro)
and find the first super exception that is pickleable. It does
not go below :exc:`Exception` (i.e. it skips :exc:`Exception`,
:class:`BaseException` and :class:`object`). If that happens
you should use :exc:`UnpickleableException` instead.
:param exc: An exception instance.
:returns: the nearest exception if it's not :exc:`Exception` or below,
if it is it returns :const:`None`.
:rtype :exc:`Exception`:
cls = exc.__class__
getmro_ = getattr(cls, "mro", None)
# old-style classes doesn't have mro()
if not getmro_: # pragma: no cover
# all Py2.4 exceptions has a baseclass.
if not getattr(cls, "__bases__", ()):
# Use inspect.getmro() to traverse bases instead.
getmro_ = lambda: inspect.getmro(cls)
for supercls in getmro_():
if supercls in unwanted_base_classes:
# only BaseException and object, from here on down,
# we don't care about these.
exc_args = getattr(exc, "args", [])
superexc = supercls(*exc_args)
return superexc
def create_exception_cls(name, module, parent=None):
"""Dynamically create an exception class."""
if not parent:
parent = Exception
return subclass_exception(name, parent, module)
class UnpickleableExceptionWrapper(Exception):
"""Wraps unpickleable exceptions.
:param exc_module: see :attr:`exc_module`.
:param exc_cls_name: see :attr:`exc_cls_name`.
:param exc_args: see :attr:`exc_args`
.. code-block:: python
>>> try:
... something_raising_unpickleable_exc()
>>> except Exception, e:
... exc = UnpickleableException(e.__class__.__module__,
... e.__class__.__name__,
... e.args)
... pickle.dumps(exc) # Works fine.
#: The module of the original exception.
exc_module = None
#: The name of the original exception class.
exc_cls_name = None
#: The arguments for the original exception.
exc_args = None
def __init__(self, exc_module, exc_cls_name, exc_args, text=None):
self.exc_module = exc_module
self.exc_cls_name = exc_cls_name
self.exc_args = exc_args
self.text = text
Exception.__init__(self, exc_module, exc_cls_name, exc_args, text)
def restore(self):
return create_exception_cls(self.exc_cls_name,
def __str__(self):
return self.text
def from_exception(cls, exc):
return cls(exc.__class__.__module__,
getattr(exc, "args", []),
def get_pickleable_exception(exc):
"""Make sure exception is pickleable."""
nearest = find_nearest_pickleable_exception(exc)
if nearest:
return nearest
except Exception:
return UnpickleableExceptionWrapper.from_exception(exc)
return exc
def get_pickled_exception(exc):
"""Get original exception from exception pickled using
if isinstance(exc, UnpickleableExceptionWrapper):
return exc.restore()
return exc
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