exec_hack.py

class MyDict(dict):
    def __init__(self):
        self._dict = {}

    def __getitem__(self, k):
        print(f'Looking up {k}')
        return self._dict[k]

    def __setitem__(self, k, v):
        print(f'Assigning {k} to {v}')
        self._dict[k] = v


locals = MyDict()
globals = MyDict()

exec('a = 42', globals, locals)
exec('b = a ** 2', globals, locals)
print(locals._dict)

# Prints this:

# Assigning a to 42
# Looking up a
# Assigning b to 1764
# {'a': 42, 'b': 1764}