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Hi and welcome back.
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In this video, we're going to talk about yapf.
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Yapf is a Python formatter, in fact it stands
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for Yet Another Python Formatter and it's used for things
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that a linter wouldn't really catch,
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but that are important still.
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For example, you've got here some code that I've written.
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And if you've been developing in Python for a while,
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you may see somethings that are just a bit weird.
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For example you got a list here, this is fine,
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you've got two elements and then, you've got another
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element and a new line which maybe okay.
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Then you've got an element in a new line
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but is less indented than the previous element.
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You've got four loop here that has a colon this time,
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but then the body is on the same line.
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This is okay in Python, it's just a bit strange.
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Then you've got a print statement, this is, we're done here.
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But, it's using single quotation marks and it's escaping
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another single quotation mark inside it.
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It would probably be better
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to use double quotation marks here instead.
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But, hey this is fine, this is Python code that actually
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works, you know, we can run it.
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Run app py, you can see that things have printed out.
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So this all okay, the linter wouldn't necessarily complain,
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although, it would complain about the missing doc string.
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They always complain about that.
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But what about the format, right?
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Well the format is also important.
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You want all the code within a project
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to have consistent format.
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The reason for that is so that as you go from one file
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to another it looks the same.
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You're not encountering any jarring experiences that are
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a bit strange, and also so that everybody working
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on the project, if you're working with more people,
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has the same standards of what a good style is
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or what the style project is.
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That way you're not going to, sort of, go from one file
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to another and be able to know who wrote it,
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just from what the code looks like.
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Everybody should have a consistent style
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so that the code base is the same for everyone
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and it doesn't feel, some files
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don't feel wrong to some people.
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For that, you have the formatters.
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The formatters you can, sort of, customise them
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and tell them what style you want and then all you do
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is run your files through the formatter and it will change
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the files such that they are still valid Python code,
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but sort of, rearrange the elements around to match a style
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that everyone in your team likes.
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So, if we go back to the terminal,
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what you're going to do is, once again,
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you're going to do ptp3.6 or ptp3 depending
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on how many versions of Python you've got installed.
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Instal yapf, yet another python formatter.
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You're going to instal that and in my case,
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it's already installed, possibly was installed
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in a different Python version and then all you have
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to do is run yapf and see if something happens.
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What will happen normally with yapf is it will just hang.
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Which is not a very nice way of running a programme,
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but because yapf needs a file to format.
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If you don't give it, I'm not really sure what's it's doing,
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but it just seems to hang up.
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So if that happens just press control and C and that will
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terminate the programme and then you can run it again
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and give it the file that you want to format
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and when you run that it's going to give you the new file.
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So this is what the file should look like according to yapf.
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As you can see all the elements are in one line
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and you've got a new line after the four loop.
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Notice that yapf has not changed the single quotation marks
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to double quotation marks, just because it's got
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an inner escaped quotation marks.
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So yapf hasn't really cared about that,
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and you know I can get behind that.
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I think this is okay, but there are other formatters
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that would change that.
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So if you like this, then you can just do yapf--help
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and it will tell you the different options
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you can give yapf.
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So you can use -h or --help to bring this help message up.
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v or --version to see what version of yapf you've got.
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Then you've got -d or --dif, either of these two options
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is valid to print out the difference between you're local
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file and the file the yapf is creating
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and you've got another one recursive in place and so forth.
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Really the one we're interested in is the in place.
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This is going to make changes to the file.
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So if we do yapf-I app.py, nothing seems to happen.
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When we go back to pycharm you can see
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that the file has changed.
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Now we got everything in one line and this is in two lines.
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If you do decide to use pycharm,
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pycharm comes with its own formatter,
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so if we do this, you'll see that pycharm actually tells
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us that you're doing something a bit weird here.
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PEP 8 continuation line under indented for visual indent.
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You find that visual indent means that this isn't a required
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indent in Python, just a visual thing and it tells
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you according to PEP 8, which is the, sort of,
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style guide for Python this is a strange thing to do.
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It also tells you here PEP 8 multiple
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statements in one line.
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So the four is one statement that prints another
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statement that is telling you shouldn't do this.
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And also, by the way, you can then put a semicolon
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and put more statements in there if you want,
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it's going to tell you again this not something
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you want to do.
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This is not something all people know about Python,
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you can use semicolons in Python as well,
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just like you can in Java
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and JavaScript to separate multiple statements in one line,
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but it's a bit weird.
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What you can do in pycharm, though, is that you can select
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everything and then you can go to code
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and you can go to reformat code
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and it'll format it if it can.
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So, once again that reformat code
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and that will do what it can.
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I'm not sure what altering net lines
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is going to do, nothing.
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So has you can see it didn't quite fix this problem here
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and that's because depending on the formatter
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it will consider some things to be fixable, sort of,
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if you do this pretty much any formatter will tell you.
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You're definitely doing something
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you don't want to do there.
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But if you do this, in some cases you may want to do this.
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In this case, pycharm's formatter
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doesn't change it for you, yapf does.
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So that's just a difference between formatters and there
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are ways of customising the formatters.
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Yapf can be customised, I'm not sure if pycharm
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can be customised too, actually.
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To make it change it if you want.
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We're not going to go into that in this course, though,
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that's for something for you to investigate if you want
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to customise it more to your needs, but of course,
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the little grey lines in pycharm still tell you where
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you're doing something a bit strange and in that case
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you can just fix it manually, if you want.
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So that's it, that's how you use the pycharm
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formatter and also yapf.
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I'm gonna put another link to another
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formatter that is up and coming called black,
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that is more strict, if you wish.
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It will change more things,
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but allegedly for a nicer end experience.
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So I'll put a link on that in the lecture
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so you can give it a go if you want.
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That's it for this video, though.
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Hope you've enjoyed it, and I'll see you on the next one.