Upload images to Google App Engine(GAE) with Flask

As you understood, this article is about uploading images to GAE. Actually, this article is mostly for beginners and covers only basic concepts, but when i started to learn GAE platform i missed such kind of tutorial a lot. So, to get started, let's take app from my previous GAE tutorial from here.
I decided to add our photo upload functionality as a separate python module and wrap it in flask blueprint. Let's create it inside of gae_flask_app dir and name it upload_photo. It would be great for you to get familiar with my previous article to deal with gae_flask_app structure.

javascript functions partial evaluation

Recently i discovered a very useful and powerful feature - functions partial evaluation. This feature comes from functional programming languages, and gives us possibility to init some functions arguments before calling this function itself.
At first,  i looked at existing implementations in some popular frameworks - such as underscore e  t. c. and find out, that there is no magic in implementing this. After that i looked at some simple implementations,  they were quite good, but had some limitations, so i decided to upgrade them to get what i wanted.  Here are some of implementations that i found :