Make the symmetric-enc example an example

Making some minor tweaks to the doc example for symmetric encryption so
it is an actual, runable example.

1 files changed, 3 insertions, 1 deletions

diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 8d3769f5..83230287 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -35,10 +35,12 @@ in an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
 
     .. doctest::
 
+        >>> import os
         >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
         >>> from cryptography.hazmat.backends import default_backend
         >>> backend = default_backend()
-        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
+        >>> key = os.urandom(24)
+        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(os.urandom(16)), backend=backend)
         >>> encryptor = cipher.encryptor()
         >>> ct = encryptor.update(b"a secret message") + encryptor.finalize()
         >>> decryptor = cipher.decryptor()