Beginning Python - From Novice to Professional

CHAPTER 1 ■ INSTANT HACKING: THE BASICS 11
>>> 1.0/2
0.5
>>> 1/2.
0.5
If you’d rather have Python do proper division, you could add the following statement to
the beginning of your program (writing full programs is described later) or simply execute it in
the interactive interpreter:
>>> from __future__ import division
Another alternative, if you’re running Python from the command line (e.g., on a Linux
machine), is to supply the command-line switch -Qnew. In either case, division will suddenly
make a bit more sense:
>>> 1 / 2
0.5
Of course, the single slash can no longer be used for the kind of integer division shown
earlier; but there is a separate operator that will do this for you—the double slash:
>>> 1 // 2
0
The double slash consistently performs integer division, even with floats:
>>> 1.0 // 2.0
0.0
There is a more thorough explanation of the __future__ stuff in the section “Back to the
__future__,” later in this chapter.
Now you’ve seen the basic arithmetic operators (addition, subtraction, multiplication,
and division), but one more operator is quite useful at times:
>>> 1 % 2
1
This is the remainder (modulus) operator—x % y gives the remainder of x divided by y.
For example:
>>> 10 / 3
3
>>> 10 % 3
1
>>> 9 / 3
3
>>> 9 % 3
0
>>> 2.75 % 0.5
0.25