Editing Community Data Science Course (Spring 2015)/Day 1 Tutorial (section)

==Booleans==

Please return to the interactive Python interpreter for the rest of the tutorial. And remember: type out the examples. You'll thank yourself tomorrow. :)

[[File:Scales.png|100px]]

So far, the code we've written has been <i>unconditional</i>: no choice is getting made, and the code is always run. Python has another data type called a '''boolean''' that is helpful for writing code that makes decisions. There are two booleans: <code>True</code> and <code>False</code>.

 True

 type(True)

 False

 type(False)

You can test if Python objects are equal or unequal. The result is a boolean:

 0 == 0

 0 == 1

Use <code>==</code> to test for equality. Recall that <code>=</code> is used for <i>assignment</i>.

This is an important idea and can be a source of bugs until you get used to it: '''= is assignment, == is comparison'''.

Use <code>!=</code> to test for inequality:

 "a" != "a"

 "a" != "A"

<code>&lt;</code>, <code>&lt;=</code>, <code>&gt;</code>, and <code>&gt;=</code> have the same meaning as in math class. The result of these tests is a boolean:

 1 > 0

 2 >= 3

 -1 < 0

 .5 <= 1

You can check for containment with the <code>in</code> keyword, which also results in a boolean:

 "H" in "Hello"

 "X" in "Hello"

Or check for a lack of containment with <code>not in</code>:

 "a" not in "abcde"

 "Perl" not in "Python Workshop"