Some more details on the impact of the bug. It affects all TLS connections from both Python 2.7 and Python 3.5. For TLS only the prime256v1 (aka secp256r1 or NIST P-256) elliptic curve is used by default (it can be changed manually). This results in handshake failures when this cipher is not supported by the server (like when the server uses a secp384r1 certificate).
With the patch from Python bug 29697 automatic curve selection is used, resulting in better curve support. I am not aware of any concrete security implications, though this issue causes the client to disregard any other preferred curves.
