Python in a Nutshell

Data Types

The operation of a Python program hinges on the data it handles. All data values in Python are represented by objects, and each object, or value, has a type. An object’s type determines what operations the object supports, or, in other words, what operations you can perform on the data value. The type also determines the object’s attributes and items (if any) and whether the object can be altered. An object that can be altered is known as a mutable object, while one that cannot be altered is an immutable object. I cover object attributes and items in detail later in this chapter.

The built-in type( obj ) accepts any object as its argument and returns the type object that represents the type of obj. Another built-in function, isinstance( obj,type ), returns True if object obj is represented by type object type; otherwise, it returns False (built-in names True and False were introduced in Python 2.2.1; in older versions, 1 and 0 are used instead).

Python has built-in objects for fundamental data types such as numbers, strings, tuples, lists, and dictionaries, as covered in the following sections. You can also create user-defined objects, known as classes, as discussed in detail in Chapter 5.

Numbers

The built-in number objects in Python support integers (plain and long), floating-point numbers, and complex numbers. All numbers in Python are immutable objects, meaning that when you perform an operation on a number object, you always produce a new number object. ...