nested scopes in python | Python Fiddle

from collections import MutableMapping

class Scope(MutableMapping):
    def __init__(self, parent=None):
        self._parent = parent
        self._scope = {}
    
    def __getitem__(self, key):
        if key in self._scope:
            return self._scope[key]
        elif self._parent is not None:
            return self._parent[key]
        else:
            raise KeyError(key)
            
    def __setitem__(self, key, value):
        self._scope[key] = value
    
    def __delitem__(self, key):
        del self._scope[key]
    
    def __iter__(self):
        for key in self._scope:
            yield key
            
        if self._parent is not None:
            for key in iter(self._parent):
                yield key
        
    def __len__(self):
        return len(self._scope) + len(self._parent) if self._parent else 0

def __repr__(self):
        return repr(dict(self))
    
    def __getattr__(self, key):
        return self.__getitem__(key)    	
    
A = Scope()
B = Scope(A)

A['hello'] = 'hi there'

print A['hello']
print B['hello']
B['hello'] = 'goodbye'

print A['hello']
print B['hello']

print A
print B

print A.hello
B.hello = 'good morning'
print B

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