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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_css_class(css_classes, css_class, prepend=False):
 """ Add a CSS class to a string of CSS classes """

    classes_list = split_css_classes(css_classes)
    classes_to_add = [c for c in split_css_classes(css_class) if c not in classes_list]
    if prepend:
        classes_list = classes_to_add + classes_list
    else:
        classes_list += classes_to_add
    return " ".join(classes_list)