How to implmement TLS Public Key Pinning in Python (Sort of modeled after HKPK)

validate_ssl_pin.py

import urllib3
from urllib3 import HTTPSConnectionPool
import certifi
import base64
import M2Crypto
import hashlib


class TestHTTPSConnectionPool(HTTPSConnectionPool):
    def _validate_conn(self, conn):
        super(TestHTTPSConnectionPool, self)._validate_conn(conn)
        pinset = [
            'c22be239f483c08957bc106219cc2d3ac1a308dfbbdd0a365f17b9351234cf00'
            ]
        if not conn.is_verified:
            return False

        der = conn.sock.getpeercert(binary_form=True)
        x509 = M2Crypto.X509.load_cert_string(der, M2Crypto.X509.FORMAT_DER)
        mem = M2Crypto.BIO.MemoryBuffer()
        public_key = x509.get_pubkey().get_rsa().save_pub_key_bio(mem)
        pk_der = mem.getvalue().split("\n")[1:-2]
        pk_base64 = ''.join(pk_der)
        pk_raw = base64.b64decode(pk_base64)
        pk_sha265 = hashlib.sha256(pk_raw).hexdigest()

        if pk_sha265 in pinset:
            pass
        else:
            raise Exception("Public Key not found in pinset!")

pool = TestHTTPSConnectionPool(
    'example.com',
    443,
    cert_reqs='CERT_REQUIRED',
    ca_certs=certifi.where())

rv = pool.urlopen('GET', 'https://example.com/')
print rv.data