Can I POST data with python requests lib with http-gzip or deflate compression?

I can't get this to work, but you might be able to insert the gzip data into a prepared request:

#UNPROVEN
r=requests.Request('POST', 'http://httpbin.org/post', data={"hello":"goodbye"})
p=r.prepare()
s=StringIO.StringIO()
g=gzip.GzipFile(fileobj=s,mode='w')
g.write(p.body)
g.close()
p.body=s.getvalue()
p.headers['content-encoding']='gzip'
p.headers['content-length'] = str(len(p.body))  # Not sure about this
r=requests.Session().send(p)

# Works if backend supports gzip

additional_headers['content-encoding'] = 'gzip'
request_body = zlib.compress(json.dumps(post_data))
r = requests.post('http://post.example.url', data=request_body, headers=additional_headers)

For python 3:

from io import BytesIO
import gzip

def zip_payload(payload: str) -> bytes:
    btsio = BytesIO()
    g = gzip.GzipFile(fileobj=btsio, mode='w')
    g.write(bytes(payload, 'utf8'))
    g.close()
    return btsio.getvalue()

headers = {
    'Content-Encoding': 'gzip'
}
zipped_payload = zip_payload(payload)
requests.post(url, zipped_payload, headers=headers)

I've tested the solution proposed by Robᵩ with some modifications and it works.

PSEUDOCODE (sorry I've extrapolated it from my code so I had to cut out some parts and haven't tested, anyway you can get your idea)

additional_headers['content-encoding'] = 'gzip'
s = StringIO.StringIO()
g = gzip.GzipFile(fileobj=s, mode='w')
g.write(json_body)
g.close()
gzipped_body = s.getvalue()
request_body = gzipped_body

r = requests.post(endpoint_url, data=request_body, headers=additional_headers)