OOP Python 3

Question

Can anyone please explain this
In a python file I have a variable named abc. It may be a string, list or any other object
If I call a method like strip() [if it's a string] or append() [if it's a list]
where the functions are defined and how they are called.
If we create a class A() which contains a method xyz(), we create a instance of that class say inst = A() and call inst.xyz() to access that method.
So my question is what happens when we don't define any class or metod and call starigway like the following
abc.append()
str.upper()
etc etc

Answer 1

Python has some predefined classes for lists, strings, integers, etc (every supported type has a corresponding class.) You are calling the methods of those classes.