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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 get_curie(self, uri):
        '''Get a CURIE from a URI '''
        prefix = self.get_curie_prefix(uri)
        if prefix is not None:
            key = self.curie_map[prefix]
            return '%s:%s' % (prefix, uri[len(key):len(uri)])
        return None