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Python Virtual Environment Simple Project Setup

Prerequisites and requirements

  • Have python 3 (recommended to use version 3.6 and above) installed in your machine. Make sure it is executable and confirm it by entering the shell or executing a python script file.
  • Make sure the pip is also installed and the commands are available. It should be included when python is installed.
  • Some fresh Linux installation will require installing the virtualenv tool using sudo apt install python3-venv.

About the demo

We are going to create a simple rest api project using FastAPI framework by utilizing the virtualenv.

Initialize virtualenv in a project directory

Let’s create a directory/folder anywhere on your machine named simple_restapi for our root project directory. Open your command prompt or terminal, go inside the directory and execute this python command:

python -m venv .venv

it will create a .venv folder inside the simple_restapi directory.

Activating the virtualenv

For Windows users, you can execute this from the simple_restapi directory:

.venv\Scripts\activate

For Unix/Linux users:

source ./.venv/bin/activate

Once the virtualenv is activated, it will create a virtual session indicating the python environment is changed and it is isolated from your machine’s python environment.

Installing dependencies

Make sure you are inside the virtualenv session because we are going to install packages for our project only. Here are the dependencies needed for our fastapi project and execute them:

pip install fastapi
pip install "uvicorn[standard]"

Check if those packages are listed using pip list command.

Simple REST API example

We could use the example script from the fastapi documentation, and create a file named main.py in the project root directory and fill it with this script: 

from typing import Union
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"Hello": "World"}

@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}

Starting the server

Still inside the virtualenv session and the root project folder, we could run the project using uvicorn:

uvicorn main:app --reload

You could test the API by accessing it in your browser (GET endpoints only) by accessing http://localhost:8000/ or using API platforms like Postman or cURL.

You can stop the server later by executing Ctrl + C

Exporting the environment

Exporting the list of packages used in the environment is essential for deploying it later in another machine. You can use pip command and redirection operator > combination:

pip freeze > requirements.txt

Importing the environment

Later when you set up the project on another machine, you can use the created requirements.txt to install dependencies:

pip install -r requirements.txt

Deactivating the virtualenv

To exit the virtualenv, you can use this command:

deactivate .venv