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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def minusExtras(self):
 """ Return a new Filter that's equal to this one, without extra terms that don't add meaning. """

        assert self.isOpen()
        
        trimmed = self.clone()
        
        equals = {}
        
        for test in trimmed.tests:
            if test.op == '=':
                equals[test.property] = test.value

        extras = []

        for (i, test) in enumerate(trimmed.tests):
            if test.op == '!=' and equals.has_key(test.property) and equals[test.property] != test.value:
                extras.append(i)

        while extras:
            trimmed.tests.pop(extras.pop())

        return trimmed