The load_pem_x509_certificate() function from cryptography can be used to
extract the public or private keys from a x509 certificate in PEM format.
# Python 2
from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.backends import default_backend
cert_str = "-----BEGIN CERTIFICATE-----MIIDETCCAfm..."
cert_obj = load_pem_x509_certificate(cert_str, default_backend())
public_key = cert_obj.public_key()
private_key = cert_obj.private_key()# Python 3
from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.backends import default_backend
cert_str = "-----BEGIN CERTIFICATE-----MIIDETCCAfm...".encode()
cert_obj = load_pem_x509_certificate(cert_str, default_backend())
public_key = cert_obj.public_key()
private_key = cert_obj.private_key()