Write short notes on Identifiers with reference to Python language.

An identifier is a component of a programming statement (token) defined with a name to identify a block (i.e., a set of indented statements). A function name, a class name or a variable name are also referred to as identifiers. For example, in the statement n = 25, n is a variable name which refers to a specific identifier. Since Python is case sensitive, Num and num are considered to be two different identifiers.