Python 3, an Illustrated Tour Transcripts
Chapter: The standard library
Lecture: Enum

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0:00 In this video, we're going to talk about the enum library, this came in Python 3.4 with Pep 435.
0:06 In the pep we read, enumeration is a set of symbolic names bound to unique constant values.
0:11 Within an enumeration, the values can be compared by identity and the numeration itself can be iterated over.
0:18 If you're not familiar with enumerations in other languages, they allow you to hard-code magic numbers and make use of those
0:24 and you could do that in Python prior by making globals and making all capitalized variable name and setting equal to some value.
0:32 There are a few features that enumerations have that make them slightly better to use. Here's an example.
0:37 I'm going to import the enum class from the enum module and then I just define a class in this case, I'm going to define a class called bike
0:45 and there are various types of bikes. So there might be a road bike or mountain biker or a cross bike or a trike.
0:50 and maybe I'm going to be switching on these different bike types or whatnot. Inside of my class, as attributes I say road is equal to 1,
0:58 mountain is equal to 2, etc. And I can define numbers that give values for those.
1:05 If you want to enumerate all the different possibilities of what are in a bike you can loop over that and you can say
1:12 well there's road, mountain, cross and trike, you can also do comparisons using the equality operator. So the last bike in the enumeration was trike,
1:21 and is that equal to a bike.trike, yes, that is the case. Trike is I believe number 4 here so you could say is bike equal equal to 4.
1:32 That's what we're trying to get around. We're trying to get around magic numbers where you're using number that has a unique meaning for you,
1:39 but maybe to someone else who's reading it doesn't make sense. So bike.trike is very explicit and makes the code more readable.
1:46 If we want to access these enumerations, you can access them in different ways so you can do the by attribute, so you can just say .mountain
1:54 you can also say bike 2, you can call it and pass in 2 and that will give you what the enumeration is. You can also do it by index name.
2:04 So there's an index operation that says mountain and that gives you back the enumeration. All these are the same.
2:11 I prefer this first one I think it's the most readable. Identity comparisons also work with enumerations as well.
2:16 So you can say bike.mountain is bike.mountain and that is true. So it's not going to make a new instance of those.
2:22 There's an alternate construction that we can use to create enumerations here. This is similar to the named tuple construction.
2:28 We're going to make a variable here called bike or bike2, camel case
2:33 because it's class like and then we're going to pass in the name of the class here. And then we're going to pass in the different enumerations in here.
2:41 And in this case, we don't need to provide the numbers we'll get default numbers for them,
2:46 so I can say bike2 what's the 2, the 2 was in this case mountain and what is road and that was this one right here bike road, which has a value of 1.
2:58 This video discussed enumerations in Python. This is included in Python 3. This is just a little library that's meant to make your code more readable.
3:06 If you're using hard coded numbers all over the place consider using enumerations, or if you have different categorical types that you're using
3:15 consider using enumerations to make your code more readable.


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