In docs for set_ciphers method of the SSLContext class (https://docs.python.org/3.6/library/ssl.html#ssl.SSLContext.set_ciphers) there is an external link labeled OpenSSL cipher list format pointing to https://www.openssl.org/docs/manmaster/apps/ciphers.html#CIPHER-LIST-FORMAT That link is dead. I believe currently the link needs to include specific open ssl version in it and the following one works fine: https://www.openssl.org/docs/man1.0.2/apps/ciphers.html#CIPHER-LIST-FORMAT The problem is present in Python 3.6 and 3.5 docs. I haven’t checked docs for other versions. Cheers Michal