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Python Sequences

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Membership Testing

2:16 with Ashley Boucher

Learn how to determine whether your Python sequence contains a particular value or other sequence.

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    In this video, we'll be discussing membership testing, in other words, 0:00
    whether or not an item or sequence is inside another sequence. 0:02
    Membership testing uses the operators in and not in. 0:06
    Take a look at my workspace here, you can see I have a really long string, 0:10
    really an entire paragraph from the Python documentation. 0:13
    I want to know whether this documentation excerpt contains the string tuple. 0:15
    To find that out, I can use the operator in. 0:20
    The expression, 'tuple' in docs, will evaluate to true or 0:22
    false, true if tuple appears in docs, and false if it does not. 0:28
    You'll see this expression most often used in conjunction with an if statement. 0:33
    So I'm gonna add just a little bit of code to this, and 0:51
    then we're gonna run it to see what happens. 0:54
    Okay, save and run. 1:11
    Great, this tells us that the string tuple is in fact inside this longer string docs. 1:21
    Alternatively, we can use the not in operator. 1:27
    This is the opposite of the in operator. 1:29
    Not in will return true if the tested object is not in the sequence, and 1:31
    will return false if it is. 1:35
    To demonstrate this, I'll modify our example code just a little bit. 1:37
    I'll change the in operator to not in, and then I'll change our print statements. 1:42
    Now when we run this again, we should see the same result. 1:53
    Yes, the string tuple is present inside the larger string docs. 1:59
    That's the gist of membership testing. 2:03
    I've demonstrated it here with strings, but 2:05
    these operators work for all sequences. 2:07
    See the following instruction step for code examples showing how to use in and 2:09
    not in with lists and tuples as well. 2:13

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