X.509 certificates are common way to exchange and distribute public key information. For example, most Open Social containers use the OAuth RSA-SHA1 signature method, and distribute their public keys in the X.509 format.
While working on an AppEngine application, I needed to verify requests from such containers. However, there is (currently) no pure python library able of parsing the certificates. This meant that I needed extract the public key out of the certificate manually, and store it in some parsed way inside the Python code.
Fortunately, parsing public keys form a X.509 certificate and representing them as a Hex number turned out simple and easy.