1class KeepContext:
2    """
3    Context manager that receives a `django.template.Context` instance and a list of keys
4
5    Once the context manager is exited, it removes `keys` from the context, to avoid
6    side effects in later layout objects that may use the same context variables.
7
8    Layout objects should use `extra_context` to introduce context variables, never
9    touch context object themselves, that could introduce side effects.
10    """
11
12    def __init__(self, context, keys):
13        self.context = context
14        self.keys = keys
15
16    def __enter__(self):
17        pass
18
19    def __exit__(self, type, value, traceback):
20        for key in list(self.keys):
21            if key in self.context:
22                del self.context[key]
23