calling methods in python

Question

I'm new to python.I read that every identifier is an object reference in python (including primitive data types). We use object reference to call object methods. For example

a="hello world"

Here a is a reference to string object and i use this reference to call string object methods.But what I found today is that I can directly use the object itself instead of a reference. ie both a.upper() and "hello world".upper() are valid.What i need to know the underlying logic of calling an object method in python.How am I able to use both object reference and object itself to call methods. Is there a difference in above two methods??

Answer 1

Reference variables are just names for objects. "hello world" is just an unnamed object - an object doesn't need a name to call methods on it, it just needs to exist.