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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 gen_classdefs(self) -> str: """ Create class definitions for all non-mixin classes in the model Note that apply_to classes are transformed to mixins """

        return '\n'.join([self.gen_classdef(k, v) for k, v in self.schema.classes.items() if not v.mixin])