When trying to connect to a server which only supports TLS version 1.1 or 1.2, the following error is raised:
ssl.SSLError: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:598)
For some reason, the SSL version is set to ssl.PROTOCOL_TLSv1 before initialisation and an SSL context is created in __init__, making any subsequent change to ssl_version useless.
The only way to establish a successful connection is to pass a custom SSL context to the constructor.
I think ssl_version should be settable at construction time before the context is created.
I'm not sure exposing ssl_version is useful either, the documentation mentions it but it has no use after initialisation.

The following lines should also be changed:
if self.ssl_version == ssl.PROTOCOL_TLSv1:
    resp = self.voidcmd('AUTH TLS')