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.
from cryptography.x509 import load_pem_x509_certificate
cert_str = b"-----BEGIN CERTIFICATE-----MIIDETCCAfm..."
cert_obj = load_pem_x509_certificate(cert_str)
public_key = cert_obj.public_key()
private_key = cert_obj.private_key()