gistfile1.py

from __future__ import with_statement

import factory
from functools import wraps


class override_strategy(object):
    def __init__(self, strategy):
        self.strategy = strategy

    def __call__(self, func):
        @wraps(func)
        def wrap(*args, **kwargs):
            with self:
                return func(*args, **kwargs)
        return wrap

    def __enter__(self):
        self._original_strategy = factory.Factory.default_strategy
        factory.Factory.default_strategy = self.strategy

    def __exit__(self, exc_type, exc_value, traceback):
        factory.Factory.default_strategy = self._original_strategy


factory.Factory.default_strategy = 'create'

with override_strategy('test'):
    assert 'test' == factory.Factory.default_strategy

assert 'create' == factory.Factory.default_strategy


@override_strategy('test')
def foo():
    assert 'test' == factory.Factory.default_strategy
foo()

assert 'create' == factory.Factory.default_strategy