Python 3, an Illustrated Tour Transcripts
Chapter: Type Annotations
Lecture: Walk-through (part 2): Annotation Tooling

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0:00 In this video, we're going to talk about annotate 3rd and the pyannotate section.
0:05 So we're assuming that you've already done steps 1 through 4 here.
0:08 The first step is to install pyannotate,
0:11 I've got my virtual env active over here.
0:14 I'm just going to say pip install pyannotate.
0:19 Okay, the next one is to create a function test_pa that exercises
0:25 and sticks the Json output into type_info.json.
0:29 So I'm going to make a file similar to our called runpa, touch
0:37 and let's open here.
0:41 I'll split my screen here so we can see both of these.
0:45 Okay, so there's, let's open
0:52 I want this to be similar to runmt, so we'll just copy all this,
0:58 it's going to be very similar to this, but we're going to change a little bit
1:00 we're going to change the mt to pa.
1:19 Okay, if you go to the pyannotate website, it's got some boilerplate here
1:23 that we can put, we need to make this little context manager here
1:27 and we need to do our import, so we'll drop in the boiler plate here,
1:36 and let's do our import from pyannotate import.
1:44 Okay, so we import this collect types guide, we init the collect types
1:48 and then we make context manager,
1:50 with our context manager we run our code and then we dump our stats here
1:55 and according to here it says that we want to dump it into this guy type_info.json.
2:04 So we'll do that type_info.json here.
2:10 Okay, so I think we've got that part.
2:15 We've got the function test_pa, and it exercises our code,
2:20 now let's run this, we're just going to run this with Python
2:24 and then using pyannotate that should look at this type_info guy here.
2:30 Let's just say Python, it doesn't say anything
2:36 but now it should be a type_info in here, let's just look at type info
2:38 and it looks like it makes sense, when we call character.speed,
2:42 it should return an int and it had one sample in there, it looks okay.
2:47 Force looks like it took an int and a float and returned a float.
2:51 So looks like that's doing okay,
2:54 it looks like quad was called with ints and returned floats.
2:59 So we can call pyannotate, you can just say pyannotate.h
3:03 it's going to give you a little help documentation.
3:06 Let's say pyannotate and we have and it says
3:10 I don't have type_info.json, interesting,
3:13 we got to change our name here, type_info.json.
3:29 Okay, and now if we run it, we get this little guy here
3:33 and it says this is the refactor, this is the diff that it would make
3:38 and note that it's making Python 2 comments here
3:41 instead of doing the Python 3 annotations.
3:45 So this is a supported syntax for Python 2
3:48 and at the end it says note that this was a dry run
3:51 we can use -w to actually write the file.
3:54 So let's use -w to write the file here.
3:57 And if we look at py3pa now,
4:00 he's got the type annotations in the comments here, cool.
4:04 And it says run mypy against py3pa, let's run mypy against this
4:08 and see what complaints we get here.
4:12 Okay, no complaints there,
4:14 we'll just turn on the strict and see if strict complains about anything else.
4:18 So that says we are still missing some stuff,
4:20 and so this shows the gradual typing of mypy
4:25 that it only checks what's annotated
4:28 and we could go in and add these other annotations,
4:31 we saw how to do that previously,
4:33 but luckily pyannotate gives us a little leg up
4:37 if we've got tests or something that we can run and get that information in there,
4:41 that will just give us a little head start to get that running.
4:43 Another benefit of this pyannotate code again is that it works in Python 2 & 3.