Displaying Blob Images in Python (App Engine)

Question

I am unable to get the image to display on the page. I can store it just fine.

These are the handlers:

class disp_image(webapp.RequestHandler):
    d         


        

Answer 1

For one, I think you're mixing up the image key and the image binary data.

The Template

You should be writing the image key (string) to your template:

 <img src="/disp?key={{image_key}}" />

i.e. your final html should look like the following if you just pass image.key() to your template:

 <img src="/disp?key=AC3CK3333KCCK2K213" />

You can think of it as a two step process. You render your template. The user browser renders the html and does a get to your image handler. The image handler then sends the binary data.

(Btw, I was under the impression you close your html tags with either <img ... /> or <img ...></img>, not both <img .../></img>)

Image Handler

In your image handler, disp_image, you should be returning the binary data of the image. It looks like you first condition is okay, but I think your else condition will just return the text "/static/unknown.gif" and not the actual binary data of the gif file.

    else:
        self.response.headers['Content-Type'] = "image/png"
        return self.response.out.write("/static/unknown.gif")

You should either store unknown.gif in your datastore and refer to it by key or you should be writing the "/static/unknown.gif" url to your template in lieu of "/disp?key=..."

Lastly, the simplest way to test whether your image handler is working is when you plug in <domain>/disp?key=... into your browser URL bar, it should load the desired image.

Answer 2

You do not have to serve images yourself. Google can do the job with Google High-Performance Image Serving for free! See: https://developers.google.com/appengine/docs/python/images/functions get_serving_url(blob_key, size=None, crop=False, secure_url=None) Where you only have to get the serving url once and save it for use in your HTML templates in your Images model class.

Answer 3

I am not sure, but I think you should not return from the get method at the disp_image class.

class disp_image(webapp.RequestHandler):
    def get(self):
        key = self.request.get('key')
        image = Images.get(key)
        if image:
            self.response.headers['Content-Type'] = "image/png"
            self.response.out.write(images.image)
        else:
            self.response.headers['Content-Type'] = "image/png"
            self.response.out.write("/static/unknown.gif")

Could you explain where is the template rendering called from? Where are you passing the image attribute?