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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 _check_pwm_list(pwm_list):
 """Check the input validity """

    for pwm in pwm_list:
        if not isinstance(pwm, PWM):
            raise TypeError("element {0} of pwm_list is not of type PWM".format(pwm))
    return True