Fix "Do you want the application "python" to accept incoming network connections?" by code signing the python executable in your virtualenv - copied here in case https://www.darklaunch.com/2014/02/02/fix-do-you-want-the-application-python-to-accept-incoming-network-connections ever goes away.

certificate_python_conections_firewall.txt

With the OS X firewall enabled, you can remove the "Do you want the application "python" to accept incoming network connections?" message.

Create a self-signed certificate.

Open Keychain Access. Applications > Utilities > Keychain Access.
Keychain Access menu > Certificate Assistant > Create a Certificate...
Enter a Name like "My Certificate".
Select Identity Type: Self Signed Root
Select Certificate Type: Code Signing
Check the Let me override defaults box
Click Continue
Enter a unique Serial Number
Enter 7300 for Validity Period.
Click Continue
Click Continue for the rest of the dialogs
Now sign your application

  codesign -s "My Certificate" -f $(which python)

In the dialog that appears, click "Allow".

Note that when using a virtual environment, you need to activate the virtual environment before running this command.

Useful for a virtual environment where connections are being refused (Mac OSX).