Create an API with FastAPI

Use FastAPI to create RESTful APIs in Python and deploy them in Saturn Cloud
Try this example in seconds on Saturn Cloud

What is an API?

A restful API is a way for programs to communicate with each other. They work similarly to websites, but instead of a human typing in a url and getting an HTML page back, a program can send a similar request to a URL and get different types of data back. For more information about APIs check out this page.

What is FastAPI?

FastAPI is a python based web framework for building Rest APIs . It does live up to its name–it is as fast as NodeJS and Go. It has inbuild data validation and as automatic document generation feature so humans can understand your API design.


In the code below we are building an API as Python scripts (.py files). Its endpoints are “/” and “/predict”, the latter one uses the data added as part of the url. The response containing result will be returned in a Python dictionary which gets converted to JSON. This implementation is utilizing FastAPI, but you can try other web frameworks like Django, Flask, Falcon as well.

Building an API

First we will import necessary libraries and create a FastAPI instance and initialize it to variable app. You can start a Saturn Cloud Jupyter Server and work on the .py script yourself. Check Create a Resource to learn how to create a resource and use Jupyter on Saturn Cloud.

from fastapi import FastAPI, HTTPException
import pandas as pd
from sklearn.linear_model import LinearRegression

app = FastAPI()

In following code we are building a regression model. The data for same is taken from Kaggle. We will be accepting number of bedrooms and year build as inputs to predict house price.

df = pd.read_csv(
lr = LinearRegression()[["BedroomAbvGr", "YearBuilt"]], df["SalePrice"])

Now we will define operation and path . Here we have used GET operation (read data) on both the paths, / and /predict. At endpoint /, we are simply redirecting request to endpoint /docs, which are the interative docs pages of FastAPI. In this documentation UI you can enter the required values and trigger response.

At endpoint /predict, we are predicting the price of house. To get the inputs from the client, we are using query parameters. Here we are passing BedroomAbvGr for number of bedrooms and YearBuilt for the year house was built. We are returning HTTP response 400 if parameters passed are not in range of training data. If the parameters fall within valid range, API will return the response as a JSON object which gives us predicted house price.

async def docs_redirect():
    return Response("Opening the docs UI", status_code=302, headers={"location": "/docs"})

async def predict(BedroomAbvGr: int = None, YearBuilt: int = None):
    a = pd.DataFrame([[BedroomAbvGr, YearBuilt]], columns=["BedroomAbvGr", "YearBuilt"])
    v = lr.predict(a)
    if not ((0 <= BedroomAbvGr <= 8) and (1872 <= YearBuilt <= 2100)):

        raise HTTPException(
            detail="Please enter BedroomAbvGr between 0 and 8. Enter YearBuilt between 1872 and 2100",

    return {"prediction": v[0]}


Let’s name the above file Save this file in a Github repo that you can access. Now click New Deployment. It can be found on top right side of the resource page.


To run, add following to command field. Uvicorn refers to the server that will use the API we have build to serve requests and reload makes the server restart after code changes. Since the host listens on, it will be reachable on an appropriate interface address to the connection. Port 8000 is a common HTTP port for web servers

python3 -m uvicorn houseprice:app --reload --host --port 8000

Add path to file in working directory field as shown below. In the screenshot below, my file is inside repository Dashboard. If you aren’t familiar with how to set up SSH credentials and add git repositories to Saturn Cloud check here. Go to pip install and add uvicorn and fastapi. Now you are ready to deploy your API by pressing the green start button on the resource page of the deployment.

deploy command

Following is the setting for rest of the fields: Name - this is set to default as ‘your username’-dashboard Instance Count - set to default as 1 Hardware and Size - This example is small hence I have selected smallest available CPU resource. Image - set to base saturncloud image

Access Deployed API

Click the URL given in deployment detail page you will be redirected to the automatic interactive API documentation.


Enter the parameter values for BedroomAbvGr and YearBuilt. Click execute .

Another way to access deployed API is through browser. Submit the following query in your url.

In example above, the key value pairs that we see after ? are known as query parameters (BedroomAbvGr=8 and YearBuilt=2000). To access this URL you need to either:

  1. Be logged into Saturn Cloud and use your browser to go to the URL, which only works for GET requests.
  2. (recommended) add an authorization token to your HTTP request. On the Saturn Cloud settings page you’ll see your user token, which lets Saturn Cloud know that your request is authorized. Add a header to the HTTP request with the key of Authorization and the value token {USER_TOKEN} where {USER_TOKEN} is your token from the settings page. In Python you could make the request like so
import requests

user_token = "youusertoken" # (don't save this directly in a file!)
url = f''
headers={"Authorization": f"token {user_token}"}
r = requests.get(url, headers=headers)

This documentation was an attempt to walk you through steps of creating your own API and deploy it. If you want to try this API yourself, just click on the Deploy API template resource and start the deployment. All the preinstallations have already been done for you.