问如何从python中的x509证书中提取公钥？

EN

from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.backends import default_backend

cert_str = '-----BEGIN CERTIFICATE----- MIIDBTCCAe2gAwIBAgIQEsuEXXy6BbJCK3bMU6GZ/TANBgkqhkiG9w0BAQsFADAt... -----END CERTIFICATE-----';

cert_obj = load_pem_x509_certificate(str.encode(cert_str), default_backend())
public_key = cert_obj.public_key();

Traceback (most recent call last):
  File "C:\xampp1\htdocs\TestWorkPlace\TestPython\src\test1.py", line 10, in <module>
    cert_obj = load_pem_x509_certificate(str.encode(cert_str), default_backend())
  File "C:\Program Files (x86)\Python\lib\site-packages\cryptography\x509\base.py", line 43, in load_pem_x509_certificate
    return backend.load_pem_x509_certificate(data)
  File "C:\Program Files (x86)\Python\lib\site-packages\cryptography\hazmat\backends\multibackend.py", line 341, in load_pem_x509_certificate
    return b.load_pem_x509_certificate(data)
  File "C:\Program Files (x86)\Python\lib\site-packages\cryptography\hazmat\backends\openssl\backend.py", line 1175, in load_pem_x509_certificate
    raise ValueError("Unable to load certificate")
ValueError: Unable to load certificate