I haven't found a suitable solution for this problem yet.
We haven't started the development, but we chose python for various reasons. So I don't wanna switch to PHP just because of an api-sdk.
Here are my thoughts for a possible solution:

Rewrite the api-sdk in Python. It's not extremely complex. I guess it will take 3-5 days. However we have to update the sdk by ourself. And the api, for what the sdk is made for, changes a lot. 
Write a wrapper around the sdk. That enables us to call each single sdk-function by executing a php file in python like execfile(filename). 
Or I use a wrapper to make the sdk-functions accessible via url.

The sdk returns result objects (like productResult).
The problem with solution 2 and 3 is that I can't to use these result objects in python. Solution 2 & 3 have to return a JSON. So I would lose some functionality of the api.
I happy to discuss your thoughts on this.
Porting the "sdk" to Python is probably your best bet - using python-requests and a custom json deserializer should make it easy. You may also want to have a look at RestORM...
How to use an api-sdk (written in PHP) in a Python app