I can't reproduce the failure with 2.7.13 but I do encounter the same failure just now, much same as yours, 2.7.5 and 2.7.13.  I'd like to describe my situation.

I have one client process started by 2.7.13(I build it from source) and one server process started by the system Python 2.7.5.  I then get the same error as yours, failing at connect() and the authkey doesn't matter.

The reason I find is that the system Python is patched by the OS vendor, changing the default MD5 algorithm to SHA256.  So they can't communicate.  Patching the source or syncing the version works for me.