The current implementation of shared_ciphers uses the SSL_get_ciphers method. This method returns the list of configured ciphers (i.e. from the context) and not the list of ciphers shared between client and server. 

To get this list one can use the documented SSL_get_client_ciphers for OpenSSL >= 1.1.0, access ssl->sessions->ciphers directly or parse the result from the undocumented SSL_get_shared_ciphers for older versions of OpenSSL.

See also https://stackoverflow.com/questions/48717497/python-ssl-shared-ciphers-not-as-documented/48718081#48718081