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- [Narrator] Hi, and
welcome back to the course.

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In this video, we're looking
at something really cool,

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which is request parsing.

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Remember in the last video,
we looked at the PUT request

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and we determined that, if
we were creating a new item,

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we were going to use the price

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in the request's JSON payload.

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However, if we were updating the item,

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we were going to use the entire payload.

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That means that, for example,

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if the payload were to include a name,

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the item's name would change
alongside this update.

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And that may not be what we want.

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So what we're going to do
is, we're going to make sure

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that only some elements can be passed in

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through the JSON payload.

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Flask-RESTful has a really
nice way of doing this,

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which is using reqparse.

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Now, reqparse is not
part of Flask-RESTful,

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or at least the way of doing this

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is not part of Flask-RESTful.

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It was built a lot earlier

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and it was present for
command line applications

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before it was present for REST APIs.

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But it works essentially the same way,

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so once you know how to use reqparse,

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which you'll learn in this video,

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you'll be able to use it in a wide range

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of other areas as well.

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Okay, so, now that we've imported

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reqparse from Flask-RESTful,

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all we have to do is go down to the "put"

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endpoint here and what
we're going to do is say

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that parser is reqparse, request parser.

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This only initialises a new object,

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which we can use to parse the request.

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Essentially, we're going to
run the request through it

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and see what arguments match those

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that we defined in the parser.

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But, of course, we first
have to define arguments,

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so we're going to say parser.add_argument,

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and the argument's going to be price.

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And then we can also give it
a bunch of other information

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such as the type, which
is going to be float.

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Remember, we had a
problem at the beginning

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that if we passed 12.00,

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the price ended up being an
integer instead of a float.

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This should get rid of that.

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We can say required equals true

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to make sure that no request
can come through with no price.

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And finally, we can also say help equals

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"this field cannot be left blank".

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You can put any other message here.

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There's also a lot of
other different things

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that you can parse the add argument

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and we will discover them as we go along.

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Now, the parsing,

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when we actually run
this with the request,

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is going to look in the JSON payload,

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but it would also look in,
for example, form payloads,

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which we haven't looked at

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and we won't look at in this course.

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But if you have an HTML form
that sends you some data,

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you can use this request parser

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to go through the form fields as well.

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Just as a bit of trivia there.

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And finally, instead of request.get_json,

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we're going to say parser.parse_args

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and that's going to parse the arguments

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that come through the JSON payload

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and is going to put
the valid ones in data.

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Now, we've only defined price,

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so if we put any other
arguments in the JSON payload,

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they will just get erased
and we will never see them.

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Okay?

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So, that's it, really.

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I'm going to put a new line in there

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to make things a bit nicer

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and now what we've done is we have

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essentially parsed our request,

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or it will do when we run it,

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and made sure that the price element.

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the price argument is there.

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So let's go over to Postman

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and I'm going to close these things here.

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Make sure the app is running, which it is.

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And then, let's create a new item,

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which is going to be a piano.

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And I'm going to send it.

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Notice the body does have the price.

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So everything is fine.

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Now I'm going to change the body

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to be price instead of price,

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which sounds pretty much the same.

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I didn't want to say "prick" in a video,

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which I just did.

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And notice how price says "this
field cannot be left blank".

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And just so you believe me,
I'm going to change the price

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and then we're going to
go into the GET items

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and make sure that it's still $17.99.

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So the request terminated when it realised

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that the field was not there

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and that's what you would expect.

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Also, to make sure that you do believe me,

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I'm going to print(data['another'])

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which is a field inside data

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that we have not added an argument for.

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So, in other words, we've only
got an argument for price.

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We don't have an argument for another.

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And then we're going to go into Postman

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and go into the PUT method again

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and make sure the price is correct

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and I'm going to put "another" in there.

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And notice how we get a key error,

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which is the nice HTML page here.

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We get a key error "another".

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And what that means is this
thing here doesn't exist.

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Data does not have a key called "another".

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And it shouldn't, because the
only argument that we've got

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is for price, so all the other arguments,

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such as "another", just get erased

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and we will never see them.

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Okay?

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Even though "another" is
here in the JSON payload,

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we have not accepted it in the API,

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therefore it just doesn't get passed in.

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Okay, that's everything
for request parsing.

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Now I would encourage you to also do this

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in your other endpoints
where you want to make sure

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that the price is passed in

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and there's nothing else passed in.

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For example, the POST method.

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And without further ado,

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I'll see you in the very next video.