Python requests module hangs on socket connection but cURL works

I recently ran into the same issue locally, and like some comments on the original question, my code worked in windows, but not linux. After a few hours found the culprit for my case: IPv6.

The python module I was using attempts to make a socket connection with a server and was by default using IPv6. After turning IPv6 off in my linux environment (Ubuntu 18.04) with the following steps:

1. Open terminal
2. Enter: sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
3. Enter: sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1

The module worked as expected**.

**note that these steps will likely vary per environment

I faced the same problem and lost a lot of time ... In my case, the problem was as follows (guniconf.py):

workers = 1

change to:

workers = 10  # any number is greater than 1

More: There is a Flask application that serves some REST API.The application has a REST API method (let's call it A-method), which makes inside itself a call to another REST API method (let's call it B-method) using requests.post(). When the B-method is called from A-method, app hangs.As I understand it, when calling the A-method, the gunicorn worker processes it, but with the B-method, there are no more workers.

I had the same issue on macOS (Catalina) recently and it turned out to be due to IPv6.

I had to go to System Preferences -> Network -> Wi-Fi -> Advanced -> TCP/IP and change Configure IPv6 to Link-local only (there wasn't an "Off" option in the list, though this would also be applicable). Then click OK and Apply.

You can also disable altogether using:

sudo networksetup -setv6off Wi-Fi