Google App Engine. Resize only big images with get_serving_url()

I have created website where users can upload image w开发者_开发知识库ith any size.

I have served images with get_serving_url function. I have added to end of image modifiers to resize image to 200px size.

http://127.0.0.1:8080/_ah/img/dtrh0i6I_V5JGulg2_LKZw===s200

I have uploaded image 1000x800 - and all right - I have image with size 200x160

If I have uploaded image 100x50 - in result I have resized image with size 200x100. But this is not a good. I need to show original small image, if image size lower that 200px.

How to do this on Google App Engine + Python with get_serving_url?

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What you need can't be done automatically using get_serving_url.

I think the easiest way to implement that would be saving the image along with a needs_resize property and calling get_serving_url without size parameter if that is not the case (which serves the original image).