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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 set(self, class_name, state, key, value):
 """Set a single style value for a view class and state. class_name The name of the class to be styled; do not include the package name; e.g. 'Button'. state The name of the state to be stylized. One of the following: 'normal', 'focused', 'selected', 'disabled' is common. key The style attribute name; e.g. 'background_color'. value The value of the style attribute; colors are either a 3-tuple for RGB, a 4-tuple for RGBA, or a pair thereof for a linear gradient. """

        self._styles.setdefault(class_name, {}).setdefault(state, {})
        self._styles[class_name][state][key] = value