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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_typedefs(self) -> str: """ Generate python type declarations for all defined types """

        rval = []
        for typ in self.schema.types.values():
            typname = self.python_name_for(typ.name)
            parent = self.python_name_for(typ.typeof)
            rval.append(f'class {typname}({parent}):\n\tpass')
        return '\n\n\n'.join(rval) + ('\n' if rval else '')