Question

I’m trying to return a thumbnail from a blobstore. For the full image, I normally write out

<img src='img?img_id=%s'></img>" % greeting.key()

(where greeting is in a loop getting a selection of images from the database) with a handler ('/img', ImageHandler) and function

class ImageHandler(webapp.RequestHandler):
def get(self):
    greeting = db.get(self.request.get("img_id"))
    if greeting.picture:
        self.response.headers['Content-Type'] = "image/png"
        self.response.out.write(greeting.picture)
    else:
        self.error(404)

This works great. However, when using get_serving_url, calling

<img src='img?img_id=%s'></img>" % (images.get_serving_url(greeting.key(), 32))

I get a TypeError: object of type 'Key' has no len(). I can only assume the blob key I used is incorrect, but as far as I know, that is the blob key.

Answer 1

You probably want to call str() on the key object before passing it to get_serving_url(). It’s most likely expecting the string form of the key.

The reason it worked in your original version is because using the % operator with a %s format specifier automatically calls str() for you to determine the string to interpolate in.