Section 5.1. Introduction to Numbers

5.1. Introduction to Numbers

Numbers provide literal or scalar storage and direct access. A number is also an immutable type, meaning that changing or updating its value results in a newly allocated object. This activity is, of course, transparent to both the programmer and the user, so it should not change the way the application is developed.

Python has several numeric types: "plain" integers, long integers, Boolean, double-precision floating point real numbers, decimal floating point numbers, and complex numbers.

How to Create and Assign Numbers (Number Objects)

Creating numbers is as simple as assigning a value to a variable:

anInt = 1 aLong = -9999999999999999L aFloat = 3.1415926535897932384626433832795 aComplex = 1.23+4.56J

How to Update Numbers

You can "update" an existing number by (re)assigning a variable to another number. The new value can be related to its previous value or to a completely different number altogether. We put quotes around update because you are not really changing the value of the original variable. Because numbers are immutable, you are just making a new number and reassigning the reference. Do not be fooled by what you were taught about how variables contain values that allow you to update them. Python's object model is more specific than that.

When we learned programming, we were taught that variables act like boxes that hold values. In Python, variables act like pointers that point to boxes. For immutable types, you do not change the contents of the box, you just point your pointer at a new box. Every time you assign another number to a variable, you are creating a new object and assigning it. (This is true for all immutable types, not just numbers.)

anInt += 1 aFloat = 2.718281828

How to Remove Numbers

Under normal circumstances, you do not really "remove" a number; you just stop using it! If you really want to delete a reference to a number object, just use the del statement (introduced in Section 3.5.6). You can no longer use the variable name, once removed, unless you assign it to a new object; otherwise, you will cause a NameError exception to occur.

del anInt del aLong, aFloat, aComplex

Okay, now that you have a good idea of how to create and update numbers, let us take a look at Python's four numeric types.