How to build a REST API in Python with Tornado (part 2)
This is a continuation of a tutorial that was started over here. I highly recommend you go through that tutorial before coming here or none of it will make sense. With that out of the way let’s continue creating our REST API.
A slightly better server
By default whenever we make a change we have to close and restart our server which isn’t great for development so we’ll change that now.
1. Our code thus far should look like this.
2. Amend the code on line 10 to look like this:
return Application(urls, debug=True)3. Now close and start the server, if all went well you shouldn’t need to stop and start as often.
Changing Hello to Todo
Our todo list will be a list(array in JS), populated with dicts. Let’s start off by creating that main array.
1. Below all the imports add.
items = []2. Change the class name HelloHandler to TodoItems and inside the make_app() function.
3. Now amend the dict in self.write to this:
self.write({'items': items})4. Check the response in Postman and you should get this.
Adding a Todo item
1. Let’s add a new class below TodoItems but above make_app called TodoItem that inherits RequestHandler.
2. Inside TodoItem create a post method with an argument of self and add this line:
self.write({'message': self.request.body})3. Now let’s add a new endpoint to our server. Expand the urls list in make_app and add a new line to it:
("/api/item/", TodoItem)4. Your code should now look like this.
5. Go into Postman, click on the plus to create a new tab, change the GET dropdown to POST and add this url
http://localhost:3000/api/item/If we had a frontend we will send some JSON data from it to the endpoint, but as we don’t we can use Postman to simulate that.
6. Click on the Body tab beneath the url. Click on the raw radio button and change the dropdown on the right to JSON(application/json).
7. Add this code to the body:
{
"id":1,
"name": "test44"
}and press Send.
8. You should get this response:
9. You’ll notice the message looks a bit funky, that’s because Python by default doesn’t automatically convert a string to a dict, so let’s import a library to do so.
10. Add this below the two imports:
import json11. Now change the `post` method to this
self.write({'message': json.loads(self.request.body)})And click Send in Postman again.
Nice.
12. Don’t forget to save your request in postman as /item.
13. Now let’s tweak the code to actually add the dict to items. Ammend the post method to look like this.
def post(self):
items.append(json.loads(self.request.body))
self.write({'message': 'new item added'})14. Now add an item with Postman, then go back to the items request and see you’re newly added item.
Deleting a todo
The way the delete method will work is by creating a new_items list which will iterate though the list and exclude the item matches the id. We will pass the item id in the URL this time instead of the Body like with did with the post request.
1. First, let’s change the item url in make_app so that it can read id’s using regex:
(r"/api/item/([^/]+)?", TodoItem)2. Create a new method in TodoItem called delete with a self and id attribute:
def delete(self, id):
self.write({'message': id})3. Jump to Postman and create a DELETE request with this url http://localhost:3000/api/item/342, the usual headers and press send.
I’m guessing you can figure out what’s going here. By default the first argument of a method is self and the second argument is anything that will be after the `/` in the url. Currently were just showing a message for any id we place in the url, let’s change the method so it can actually delete an item.
4. Make this the first line in the delete method:
new_items = [item for item in items if item['id'] is not int(id)]This is an example of ‘list comprehension’ in Python. In Javascript the above line would be written with an array filter method like so:
const new_items = items.filter(item => item.id !== +id)And the same thing can be done in Python using Lambda a function:
new_items = filter(lambda item: item['id'] != int(id), items)Which you’re welcome to put in your actual code, but the first line of code is more readable and more Pythonic (the Python way of coding), so that’s why I would recommend doing it that way. You’re welcome to put some prints in the code to see how it works before moving on.
5. Now let's assign new items to items, and give a message telling developers what item has been deleted. Add these two pines to the bottom of the new_item variable.
items = new_items
self.write({'message': 'Item with id %s was deleted' % id})6. Unlike Javascript in Python if you want to change a global variable inside a function/method we need to use the keyword global and then the variable name we want to use in the method/function or it will give you an error. Place this code above the new_items variable since it references items.
global items7. One more tweak is required. Because our /api/item/ url has been rewritten to expect another argument the post method will no longer work since we’re just passing in self and nothing else, to fix that you can amend it like so:
def post(self, _):And with that done you’ve created your first API with Python and Tornado. This is what your finished code should look like:
Nice work! From here on out there are a few things you can do on your own:
- Add a put method to edit a Todo item
- Prevent multiple items with the same id to be added
- Create a get method to show the details of a single item
- Or if you’re a front-end dev you could create a little todo list that makes calls to your API
If you get a bit stuck I have the finished code here on Github (apart from the frontend).
As you’ve noticed if you restart the server you will lose all the todo items in your list which is not ideal. The way to fix that is to save your todo items in a database of some sort which is something I’m looking to write at some point in the future time permitting. But until then, I hope this has been a helpful introduction to Tornado and REST API’s in general.
