t.py

from cryptography.hazmat.backends import openssl, commoncrypto, default_backend
from cryptography.fernet import Fernet

def encrypt(backend):
    f = Fernet(Fernet.generate_key(), backend=backend)
    return f.encrypt(b"my deep dark secret")

print "OpenSSL Version: ", openssl.backend.openssl_version_text()
print "CommonCrypto: ", encrypt(commoncrypto.backend)
print "OpenSSL: ", encrypt(openssl.backend)
print "Default: ", encrypt(default_backend())