Including validation set in my code for a Linear SVM classifier returns a Type error
Based on the repo you linked in the comment section (github.com/prrao87/fine-grained-sentiment), method_class is meant to be a Class not an instance. Therefore method_class.predict is meant to be a static method not an instance method, Static method are declared without specifying a self (as they are not linked to an instance but a class) declaring your function as def predict(train_file: str, test_file: str, lower_case: bool) should fix your problem.
Some reference on the topic : https://www.makeuseof.com/tag/python-instance-static-class-methods/