What happens in context, stays in context.

context.py

from contextlib import AbstractContextManager
from types import SimpleNamespace


class Context(SimpleNamespace, AbstractContextManager):

    def __enter__(self):
        self._globals = dict(globals())
        globals().update(self.__dict__)
        return self

    def __exit__(self, *exc):
        for key, val in globals().items():
            if key in self.__dict__:
                self.__dict__[key] = val
        globals().clear()
        globals().update(self._globals)
        return False


a = 1
b = 1

ctx = Context(a=2, b=2, c=42)

assert a == 1
assert b == 1

with ctx:
    assert a == 2
    assert b == 2
    assert c == 42
    a += b
    assert a == 4

assert a == 1
assert b == 1
assert 'c' not in globals()

with ctx:
    assert a == 4
    assert b == 2
    assert c == 42

# Using Context like a "let" expression
with Context(a=1, b=2):
    a += b
    assert a == 3