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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 add_suffix(string, suffix):
 """ Adds a suffix to a string, if the string does not already have that suffix. :param string: the string that should have a suffix added to it :param suffix: the suffix to be added to the string :return: the string with the suffix added, if it does not already end in the suffix. Otherwise, it returns the original string. """

    if string[-len(suffix):] != suffix:
        return string + suffix
    else:
        return string