celery/celery/backends/database/a805d4bd.py

# -*- coding: utf-8 -*-
"""
    celery.backends.database.a805d4bd
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    This module fixes a bug with pickling and relative imports in Python < 2.6.

    The problem is with pickling an e.g. `exceptions.KeyError` instance.
    As SQLAlchemy has its own `exceptions` module, pickle will try to
    lookup :exc:`KeyError` in the wrong module, resulting in this exception::

        cPickle.PicklingError: Can't pickle <type 'exceptions.KeyError'>:
            attribute lookup exceptions.KeyError failed

    doing `import exceptions` just before the dump in `sqlalchemy.types`
    reveals the source of the bug::

        EXCEPTIONS: <module 'sqlalchemy.exc' from '/var/lib/hudson/jobs/celery/
            workspace/buildenv/lib/python2.5/site-packages/sqlalchemy/exc.pyc'>

    Hence the random module name 'a805d5bd' is taken to decrease the chances of
    a collision.

"""
from __future__ import absolute_import

from sqlalchemy.types import PickleType as _PickleType


class PickleType(_PickleType):  # pragma: no cover

    def bind_processor(self, dialect):
        impl_processor = self.impl.bind_processor(dialect)
        dumps = self.pickler.dumps
        protocol = self.protocol
        if impl_processor:

            def process(value):
                if value is not None:
                    value = dumps(value, protocol)
                return impl_processor(value)

        else:

            def process(value):  # noqa
                if value is not None:
                    value = dumps(value, protocol)
                return value
        return process

    def result_processor(self, dialect, coltype):
        impl_processor = self.impl.result_processor(dialect, coltype)
        loads = self.pickler.loads
        if impl_processor:

            def process(value):
                value = impl_processor(value)
                if value is not None:
                    return loads(value)
        else:

            def process(value):  # noqa
                if value is not None:
                    return loads(value)
        return process

    def copy_value(self, value):
        if self.mutable:
            return self.pickler.loads(self.pickler.dumps(value, self.protocol))
        else:
            return value