Using requests in requests_example.py, you can see by default 43 suites are sent in the Client Hello, which doesn't look anything like Chrome's 16 (or Firefox). Using set_ciphers, you can get closer, but the order isn't the same, and GREASE isn't included.
Requests https://github.com/psf/requests uses urllib3 https://github.com/urllib3/urllib3 which depends on pyOpenSSL / cryptography, which uses Python's standard library SSL module https://docs.python.org/3/library/ssl.html . It's likely to be linked to OpenSSL 1.1.1, but that probably depends on your OS.
Go has its own standard TLS library, so it was forked to make modifications https://github.com/refraction-networking/utls . You could call a Go executable from python, but that might not cleanly integrate with your existing python code.
Looking for alternative TLS libraries, Chrome uses BoringSSL, and Firefox uses NSS. BoringSSL is a fork of OpenSSL, so it should be easier to swap in than NSS.
I figured that if I built BoringSSL as a shared library, I should be able to use it from Python via ctypes/cffi/cython. I used manylinux and Github Actions to create a binary wheel and upload it to testpypi: https://github.com/jonatron/boringssl/commit/75241956b3d748888ae4906f45ded14b120dc999 . There's only a wheel for x86_64 linux python3.6 currently, but it should be widely compatible.
I validated the idea by writing a very basic HTTP1.1 client using a raw socket, in http11_client.py.
Looking at alternatives to requests, I found the excellent https://github.com/encode/httpcore and https://github.com/encode/httpx/ .
It was easy to write a NetworkBackend for httpcore, boring_backend.py is less than 150 lines total.
This isn't ready to use, for example certificate validation and closing sockets is missing.
You can try out core_h2.py by running:
python3 -m venv venv
source venv/bin/activate
pip install -i https://test.pypi.org/simple/ boringssl-binary-build
pip install -r requirements.txt
python core_h2.py
In the future, if requirements.txt breaks, use frozen_requirements.txt .