Build a web API from scratch with FastAPI — the workshop

The first FastAPI workshop at PyCon Belarus

Last weekend I had the chance to go to PyCon Belarus, I had a great time and met a lot of great people.

Creating the workshop

When creating the workshop I got a bit excited and created too much content for the time I had available.

The first version of the workshop

The speed of a workshop like this has a constant tradeoff, as there’s always people that finish some part faster than others, so, at some points some people will be “bored” while others will be stressed finishing some part before the next comes.

Source code for the final version

I don’t have an easy way to provide it step by step with all the explanations here, but if you are curious you can still check here the last version of the code.

Create a project directory

Create a directory for the project.

$ mkdir apiapp
$ cd ./apiapp/

Create a Python environment

In the ./apiapp/ directory, create a new Python environment.

$ python --version# OR$ python3.6 --version# OR$ python3.7 --version
python -m venv env

Initialize git

$ git init

Ignore that environment in git

Inside of that ./env/ directory, create a file .gitignore with the contents:


Activate the environment

Now we need to “activate” the environment.

$ source ./env/bin/activate
$ which python

Activate in Windows

If you are in Windows, in Git Bash, activate with:

$ source ./env/Scripts/activate
$ .\env\Scripts\Activate.ps1
$ Get-Command python

Deactivate an environment

We don’t need to deactivate the environment because we are going to use it. But if you need to deactivate it later, just run:

$ deactivate

Open your editor

Open your editor and select that environment.

Visual Studio Code

If you have Visual Studio Code and a shell like Bash, you can just run:

$ code ./


If you use PyCharm as your editor, open it.

Using the correct environment

Using the correct environment in your editor as we described here and opening it exactly in your project directory will make your editor know the installed packages and will let it provide autocompletion, type checks, relative imports, etc.

Create files

Now, in your editor, create a directory app. It will store all your actual code.

├── app
│ ├──
│ └──
├── requirements.txt
└── env
└── ...


Edit your requirements.txt to have the following contents:


Install requirements

Now install the requirements from that requirements.txt file in the terminal with:

$ pip install -r requirements.txt

Dev requirements

Now, to facilitate development, we’ll also add extra packages that will help us during development.


Install dev requirements

And now install the development requirements in the same way:

$ pip install -r dev-requirements.txt

In VS Code

Enable Language Server, mypy, black in the settings.

Reload editor

You might need to reload your editor for it to be able to detect the newly installed packages.

Reload environment

Right after installing new Python packages in your environment, you should activate the environment again:

$ source ./env/bin/activate
$ which uvicorn

Note: Other package managers

If you used a different environment and package manager like Poetry or Pipenv, the requirements.txt file would be a different file and it would be managed differently, but here we are using the simplest version with the pure/standard Python packages (venv, pip, etc).

The app — version 1

Now we are going to create the first version of our app.

Edit — v1

Edit the file

Run — v1

Run it:

$ uvicorn app.main:app --reload
  • Edit again, Uvicorn auto-reloads.

Final Version

The final version of the source code is here:

Additional scripts

There’s a script to run the tests and report coverage in HTML so that you can explore it in your browser:

$ bash
$ bash

About me

You can follow me, contact me, ask questions, see what I do, or use my open source code:



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Sebastián Ramírez

Sebastián Ramírez

Creator of FastAPI and Typer. Dev at Exposion AI. APIs, Deep Learning/Machine Learning, full-stack distributed systems, SQL/NoSQL, Python, Docker, JS, TS, etc.