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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_block(self, usage_id, for_parent=None):
 """ Create an XBlock instance in this runtime. The `usage_id` is used to find the XBlock class and data. """

        def_id = self.id_reader.get_definition_id(usage_id)
        try:
            block_type = self.id_reader.get_block_type(def_id)
        except NoSuchDefinition:
            raise NoSuchUsage(repr(usage_id))
        keys = ScopeIds(self.user_id, block_type, def_id, usage_id)
        block = self.construct_xblock(block_type, keys, for_parent=for_parent)
        return block