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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 del_bg(self, key):
 """Remove the background image data Parameters key: str One of :const:`VALID_BG_KEYS` """

        if key not in VALID_BG_KEYS:
            raise ValueError("Invalid bg key: {}".format(key))
        if key in self.h5["bg_data"]:
            del self.h5["bg_data"][key]
        else:
            msg = "No bg data to clear for '{}' in {}.".format(key, self)
            warnings.warn(msg)