self is not None. self refers to the instance of the class. self.left is an instance attribute that you set to None in your __init__() method when you create the instance. Because self.left refers to None and the object None does not have the inOrder() method, you obtain an AttributeError. Within your class definition, self (referring to an instance of the class) does have the inOrder() method, but it's attribute self.left (referring to None), does not.

self is not None. self refers to an instance of the class. self.left is an instance attribute that you set to None in your __init__() method when you create the instance. Because self.left refers to None and the object None does not have the inOrder() method, you obtain an AttributeError. Within your class definition, self (referring to an instance of the class) does have the inOrder() method, but it's attribute self.left (referring to None), does not.

self is not None. self refers to the instance of the class. self.left is an instance attribute that you set to None in your __init__() method when you create the instance.

self is not None. self refers to the instance of the class. self.left is an instance attribute that you set to None in your __init__() method when you create the instance. Because self.left refers to None and the object None does not have the inOrder() method, you obtain an AttributeError. Within your class definition, self (referring to an instance of the class) does have the inOrder() method, but it's attribute self.left (referring to None), does not.