def custom_input_number(prompt=''):
    """ Take in user input. This deals with real
    number only. See below for a function that deals with
    purely alphabetic strings.
    :param prompt: a customizable prompt
    :return:
        no: a real number
    """
    cF = True
    while cF:
        try:
            no = float(input(prompt))
            float(no)
            return no
        except ValueError:
            print('Cannot be converted to a string')
            continue