FastAPI - Accessing Form Data

Now we shall see how the HTML form data can be accessed in a FastAPI operation function. In the above example, the /login route renders a login form. The data entered by the user is submitted to /submit URL with POST as the request method. Now we have to provide a view function to process the data submitted by the user.

FastAPI has a Form class to process the data received as a request by submitting an HTML form. However, you need to install the python-multipart module. It is a streaming multipart form parser for Python.

pip3 install python-multipart

Add Form class to the imported resources from FastAPI

from fastapi import Form

Let us define a submit() function to be decorated by @app.post(). In order to receive the form data, declare two parameters of Form type, having the same name as the form attributes.

@app.post("/submit/")
async def submit(nm: str = Form(...), pwd: str = Form(...)):
   return {"username": nm}

Press submit after filpng the text fields. The browser is redirected to /submit URL and the JSON response is rendered. Check the Swagger API docs of the /submit route. It correctly identifies nm and pwd as the request body parameters and the form’s "media type" as apppcation/x-www-form-urlencoded.

It is even possible to populate and return Pydantic model with HTML form data. In the following code, we declare User class as a Pydantic model and send its object as the server’ response.

from pydantic import BaseModel
class User(BaseModel):
   username:str
   password:str
@app.post("/submit/", response_model=User)
async def submit(nm: str = Form(...), pwd: str = Form(...)):
   return User(username=nm, password=pwd)