Python script for uploading an image to a Google App Engine Dev Server's Blobstore from an external URL.

upload_to_blobstore.py

import requests

DEV_SERVER_HOST = 'localhost'
INSTANCE_PORT = 8080
UPLOAD_PATH = 'admin/upload'

def upload_image(url):
    def get_upload_url():
        cookies = {'dev_appserver_login': 'test@example.com:True'}
        resp = requests.get(
            'http://%s:%d/%s' % (DEV_SERVER_HOST, INSTANCE_PORT, UPLOAD_PATH),
            cookies=cookies)
        upload_url = resp.json()['message']
        return upload_url

    response = requests.get(url)
    content_type = response.headers['content-type']
    file_extension = content_type.split('/')[1]
    image = response.content
    files = {'file': ('image.%s' % file_extension, image)}
    upload_url = get_upload_url()
    response = requests.post(upload_url, files=files)
    return response.json()