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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 ensure_size( self, size = None ):
 """ This function removes the least frequent elements until the size constraint is met. """

        if size is None:
            size = self.size_constraint
        while sys.getsizeof(self) > size:
            element_frequencies = collections.Counter(self)
            infrequent_element = element_frequencies.most_common()[-1:][0][0]
            self.remove(infrequent_element)