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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 _assert_category(self, category):
 """Validate category argument"""

        category = category.lower()
        valid_categories = ['cable', 'broadcast', 'final', 'tv']
        assert_msg = "%s is not a valid category." % (category)
        assert (category in valid_categories), assert_msg