TIL: Howto create multipart form data in Python

What is a TIL?

Today I learnt how to encode data as multipart/form-data in Python. This is useful if you want to construct the body of a POST request yourself.

Once you find the answer it is surprisingly simple: encode_multipart_formdata() in urllib3.

fields = {
    "foo": "bar",
    "somefile": ("somefile.txt", "contents of somefile"),
    "imagegfile": ("cats.png", open("cats.png").read(), "image/png"),
}

body, header = encode_multipart_formdata(fields)

You can then use body as the body of your POST request and the value of header for the content-type header.

This is also a great example of why you should create "Today I Learnt"s. I had figured out how to do this a few months ago, but it still took me 30 minutes to find the bit of code I created back then. If I had written it down here it would have taken minutes.