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I've created a new Python file called 
super_sub.py for these examples. 

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A good place to start is with the animals and 
birds sets, that we've just seen in the slides: 

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Ok, the slides showed using the 
greater than and less than operators, 

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to check if one set is a 
superset or subset of another. 

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Sets also have a couple of 
methods, and I'll start with those: 

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The issubset method will return True if birds is 
a subset of animals. 

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issuperset returns True if animals is a superset of birds.
Run the program: 

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and we get the expected results. 
birds is a subset of animals, 

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which means that animals is a superset of birds.
If we do that the other way round, 

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we should get False:

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Run the program again:

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and birds isn't a superset of animals. There's 
nothing surprising about these results. 

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Let's use the operators to check:

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I haven't printed any text this time, to save time typing.
Run the program: 

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and birds is both a subset of animals, 
and a proper subset of animals. 

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Note that the issubset and issuperset 
methods check for subsets and supersets. 

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They're equivalent to using less than or equal 
to, and greater than or equal to, respectively. 

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The methods don't check for 
proper subsets or supersets. 

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I'll demonstrate that by creating a new set, and 
checking it against the birds set.

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I'll print a row of asterisks first, to separate the output:

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Ok, that's the same set as our birds set.

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Just to be sure, I'll compare the two sets:

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Run the program:

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and check that we get True. 
The two sets are equal, 

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because they both contain the same elements.
Now we can demonstrate the difference between 

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subset and proper subset:

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On line 25, we check if garden_birds is a subset of birds.
Line 26 checks if it's a proper subset. 

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That means it's a subset, but isn't the same set.
Run the program again: 

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Line 25 prints True. garden_birds 
is a subset of birds. 

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We've already checked if the sets are equal. 
They are – which means garden_birds isn't 

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a proper subset. The output from line 
26 confirms that - we get False printed. 

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You can do the same thing with supersets: use 
greater than, and greater than or equal to, 

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to check for a superset.
Alright, the last thing we should check, is what 

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happens when one set isn't a subset of another.

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I'll print another row of asterisks, and create a new set:

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The more_birds set contains Budgie, so it can't be a subset of garden_birds.

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There's no budgie in garden_birds.

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On line 31, I checked if garden_birds is 
a superset of more_birds. Run the program: 

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to make sure we get False.
There's not much else to 

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say about sets and subsets – not 
without getting all mathematical, anyway.

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And if you need to use Python 
for set theory, you've got almost 

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everything you need to perform all the set 
operations and tests that set theory uses. 

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I said almost, because there's one 
more method that you might find useful. 

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Sets also have an isdisjoint method. Sets 
are disjoint if they have no items in common. 

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Check out the isdisjoint method, when you 
read through the documentation on sets. 

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In the next video, we'll see a practical 
application of checking for subsets and supersets. 

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See you in the next video.