Add a file to a submission in the Canvas LMS API

canvas_submission_file_comment.py

import requests

token = "YOUR CANVAS API TOKEN"
filename = "test.txt"
file_url = "https://gatech.instructure.com/api/v1/courses/137794/assignments/537670/submissions/26370"
url = file_url + "/comments/files"
headers = {"Authorization": f"Bearer {token}"}

data = {
    "name": filename,
    "content_type": "text/plain",
}
res = requests.post(url, data=data, headers=headers)

with open(filename, "rb") as f:
    res = requests.post(
        res.json()["upload_url"], 
        data={"key": filename}, 
        files={"file": f}
    )

data = {
    "key": filename,
    "comment[file_ids][]": res.json()["id"],
}
res = requests.put(file_url, data=data, headers=headers)

canvas_submission_file_comment.sh

#!/bin/bash

# https://canvas.instructure.com/doc/api/file.file_uploads.html
# https://canvas.instructure.com/doc/api/submissions.html
# https://canvas.instructure.com/doc/api/submission_comments.html

token='YOUR CANVAS API TOKEN'
file='test.txt'
url='https://gatech.instructure.com/api/v1/courses/137794/assignments/537670/submissions/26370/comments/files'
file_url='https://gatech.instructure.com/api/v1/courses/137794/assignments/537670/submissions/26370'
res=$(curl -s -X POST $url \
    -F "name=$file" \
    -F 'content_type=text/plain' \
    -H "Authorization: Bearer $token")
upload_url=$(echo $res | jq -r .upload_url)
res=$(curl -s $upload_url \
    -F "key=$file" \
    -F "file=@$file")
file_id=$(echo $res | jq -r .id)
curl -s -X PUT $file_url \
    -F "comment[file_ids][]=$file_id" \
    -H "Authorization: Bearer $token" > /dev/null