Compressed multipart form (file) upload using Python requests.

compressed-multipart-python-requests.sh

In [16]: data = {'some': 'data'}

In [17]: data_compressed = gzip.compress(json.dumps(data, ensure_ascii=False).encode())

In [18]: requests.post("https://httpbin.org/anything", files={"msg": ('message.json.gz', body_compressed)}).json()

Out[18]:
{'args': {},
 'data': '',
 'files': {'msg': 'data:application/octet-stream;base64,H4sIAGeLyGIC/6tWKs7PTVWyUlBKSSxJVKoFABmPLCMQAAAA'},
 'form': {},
 'headers': {'Accept': '*/*',
  'Accept-Encoding': 'gzip, deflate',
  'Content-Length': '186',
  'Content-Type': 'multipart/form-data; boundary=c8efd8af2c6d7b1a375b14a8b548c0ef',
  'Host': 'httpbin.org',
  'User-Agent': 'python-requests/2.28.0',
  'X-Amzn-Trace-Id': 'Root=1-62c893f0-3518418039ad9996485c1bd9'},
 'json': None,
 'method': 'POST',
 'origin': '98.245.210.217',
 'url': 'https://httpbin.org/anything'}

Note that as per RFC 7578, content-encoding is not allowed; therefore the receiving app must either assume the request is always compressed, or key off the filename for the body part.