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If Statements

Mahdi Yusuf

Idiomatic Python 101
Mahdi Yusuf 01:08

if statements are used for truth value testing. In this lesson, you learned that you don’t need to explicitly compare a value to True or False, you can simply add it to the if statement:

Bad

Python 
if value == True:
    print 'truthy'

if value2 == None:
    print None

Good

Python 
if value:
    print 'truthy'

To compare a value to False, use the not operator:

Python 
if not value1:
    print 'falsy'

Explicitly check for None:

Python 
if value2 is None:
    print None

00:00 The next idiom I’d like to discuss is the if statement, so we have a few expressions here that we can use to show and illustrate the example here. First, we’ll discuss the poor way of going about it.

00:11 We have an expression that evaluates to True or False and then we run that against the if statement. Now, in Python, this is a redundant step.

00:20 We can simply check to see if the value itself is True or False. So as you can see here—let me just comment this out. As you can see here, they both evaluate the same way. This is a little bit cleaner, a little bit easier to write.

00:33 The next is to illustrate how the False statement would work. That’s simply by putting a not in front of whatever value you want to evaluate to True so that it prints 'falsy'.

00:48 And as you can see, that also works.

00:51 The next expression is the evaluation of None, which is slightly different and we’ll get into that in another talk, but to check against None, you simply use the is statement.

01:03 And that prints None.

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