Running your http_client.py against my graphql server running in strapi.js, I get this error:
POST body missing. Did you forget use body-parser middleware?
Granted, I edited the query for the particular schema that I have on that server but I was surprised since I thought that would work. I just wanted to know whether you may have had the same issue? I'm going to try one of the python graphql clients like sgqlc & I'll see how that works.