Handling forms and files

When submitting forms and uploading files, they are usually sent with the multipart/form-data encoding.

We already saw how to create data encoded in multipart/form-data, and submit it to an endpoint, but how can we handle incoming data in such a format?

How to do it...

The cgi.FieldStorage class in the standard library already provides all the machinery required to parse multipart data and send it back to you in a way that is easy to handle.

We will create a simple web application (based on WSGIApplication) to show how cgi.FieldStorage can be used to parse the uploaded file and show it back to the user:

import cgi

from web_06 import WSGIApplication
import base64

app = WSGIApplication()

@app.route('/')
def index(req, resp):
    return (
        b'<form action="/upload" method="post" enctype="multipart/form-
           data">'
        b'  <input type="file" name="uploadedfile"/>'
        b'  <input type="submit" value="Upload">'
        b'</form...