<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def set_alpha_value(self, value):
        '''
        setter
        Learning rate.
        '''
        if isinstance(value, float) is False:
            raise TypeError("The type of __alpha_value must be float.")
        self.__alpha_value = value