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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 validate_return_value(self, retval):
        '''
        Validate the return value of a function call. If an error occurred,
        the function will throw a TypesafetyError.

        The `retval` should contain the return value of the function call.
        '''

        if self.__return_annotation is None:
            return

        if not self.__is_valid(retval, self.__return_annotation):
            func_name = self.__function.__name__
            msg = self.RET_TYPE_ERROR_MESSAGE.format(
                func_name,
                self.__format_expectation(self.__return_annotation),
                retval.__class__.__name__
            )
            raise TypesafetyError(msg)