Simple APIs with Python and Flask • Jamie Phillips

My post on Polaris started out with me looking at building a simple REST API with Python. I had to pivot a little based on some other limitations, but I will revisit this now. Python is one of those languages that I can’t ever seem to use, yet I keep coming back to it. Maybe one of these days, I will get to use it more than I currently do. Flask keeps building apps simple, and I discovered this library called Flask-RESTful that is really elegant. Unfortunately, there is a GitHub issue, where one of the developers suggests using MethodViews in Flask instead. Given there hasn’t been a new release in some time, I thought it would be better to checkout MethodView.

MethodViews allow you to define a class that implements all the HTTP verbs that will serve your API resource. You can designate our routes that align with the methods in that class. It is a clean and straightforward approach that the last time I felt this way was when Nancy was released for .NET. Let’s build a simple API with Flask.

Installing Flask

We need to create a Python virtual environment, source it, then install Flask.

$ mkdir simple-api && cd simple-api
$ python3 -m venv .env
$ source .env/bin/activate
$ pip install Flask
Successfully installed Flask-1.1.2 Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 itsdangerous-1.1.0

The Code

With Flask installed, we need to create the Python file that will be our application.

$ touch api.py

Let’s open that in your favorite editor and import the modules we need, which is Flask and the MethodView

from flask import Flask
from flask.views import MethodView

Now we need to create our MethodView, which is our API resource.

class People(MethodView):
    def get(self, id):
        if id is None:
            return "Returns list of people!"
        else:
            return "Returns single person by id!"

    def post(self):
        return "Creates a new person!"

    def delete(self, id):
        return "Deletes a person by id!"

    def put(self, id):
        return "Updates a person by id!"

There isn’t much in here. We are just getting the basics in place. Now let’s create our Flask application and create our routes.

app = Flask(__name__)

people_view = People.as_view('people_api')
app.add_url_rule('/people/', defaults={'id': None},
                 view_func=people_view, methods=['GET',])
app.add_url_rule('/people/', view_func=people_view, methods=['POST',])
app.add_url_rule('/people/<int:id>', view_func=people_view,
                 methods=['GET', 'PUT', 'DELETE'])

At this point, this would be a fully functional Flask application. I like to make mine executable without the extras, so I make it executable.

if __name__ == "__main__":
    app.run(debug=True)

Here is the complete api.py file.

from flask import Flask, session
from flask.views import MethodView


class People(MethodView):
    def get(self, id):
        if id is None:
            return "Returns list of people!"
        else:
            return "Returns single person by id!"

    def post(self):
        return "Creates a new person!"

    def delete(self, id):
        return "Deletes a person by id!"

    def put(self, id):
        return "Updates a person by id!"

app = Flask(__name__)

people_view = People.as_view('people_api')
app.add_url_rule('/people/', defaults={'id': None},
                 view_func=people_view, methods=['GET',])
app.add_url_rule('/people/', view_func=people_view, methods=['POST',])
app.add_url_rule('/people/<int:id>', view_func=people_view,
                 methods=['GET', 'PUT', 'DELETE'])


if __name__ == "__main__":
    app.run(debug=True)

If you install a tool like HTTPie, we can test it out with the following commands.

Get all people

$ http http://127.0.0.1:5000/people/
HTTP/1.0 200 OK
Content-Length: 23
Content-Type: text/html; charset=utf-8
Date: Sat, 24 Oct 2020 17:38:55 GMT
Server: Werkzeug/1.0.1 Python/3.8.6

Returns list of people!

Get a single person

$ http http://127.0.0.1:5000/people/1
HTTP/1.0 200 OK
Content-Length: 28
Content-Type: text/html; charset=utf-8
Date: Sat, 24 Oct 2020 17:39:15 GMT
Server: Werkzeug/1.0.1 Python/3.8.6

Returns single person by id!

Update a person

$ http put http://127.0.0.1:5000/people/1 
HTTP/1.0 200 OK
Content-Length: 23
Content-Type: text/html; charset=utf-8
Date: Sat, 24 Oct 2020 17:40:03 GMT
Server: Werkzeug/1.0.1 Python/3.8.6

Updates a person by id!

Create a person

$ http post http://127.0.0.1:5000/people/
HTTP/1.0 200 OK
Content-Length: 21
Content-Type: text/html; charset=utf-8
Date: Sat, 24 Oct 2020 17:41:08 GMT
Server: Werkzeug/1.0.1 Python/3.8.6

Creates a new person!

Delete a person

$ http delete http://127.0.0.1:5000/people/1
HTTP/1.0 200 OK
Content-Length: 23
Content-Type: text/html; charset=utf-8
Date: Sat, 24 Oct 2020 17:41:57 GMT
Server: Werkzeug/1.0.1 Python/3.8.6

Deletes a person by id!

Conclusion

What can I say? I really like Python and many of the libraries/frameworks that are available. All of this was possible in 32 lines of code. I feel it is entirely understandable and clear where to add in the additional logic. Adding more resources would be creating a class, implementing the HTTP methods that you need, and the routes that you want those to have.

Thanks for reading,

Jamie

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