下列有关openSSL的PHP代码，如果用Python实现？

function getCertId($cert_path) {
    $pkcs12certdata = file_get_contents ( $cert_path );

    openssl_pkcs12_read ( $pkcs12certdata, $certs, SDK_SIGN_CERT_PWD );
    $x509data = $certs ['cert'];
    openssl_x509_read ( $x509data );
    $certdata = openssl_x509_parse ( $x509data );
    $cert_id = $certdata ['serialNumber'];
    return $cert_id;
}

我写了个Python的版本，使用的是pyopenssl，如下：

'''解析pfx格式的证书ID，这里针对的是签名证书'''
def getCertIdWithPFX(cert_path):
    fp = open(cert_path, 'r')
    if not fp:
        raise Exception('open %s fail!!!' % cert_path)
    pkcs12certdata = fp.read()

    '''先解析pkcs12格式'''
    sdk_sign_cert_password = config['sdk_sign_cert_password']
    certs = OpenSSL.crypto.load_pkcs12(pkcs12certdata, sdk_sign_cert_password)

    '''然后解析x509格式'''
    x509data = certs.get_certificate()
    print x509data
    cert_data = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_ASN1, x509data)
    print '-------------------', cert_data
    return cert_data.get_serial_number()

问题主要出在x509data，我该如何才能得到x509data中的数据呢，Python中这是个对象。

---

from OpenSSL.crypto import load_pkcs12, FILETYPE_PEM, PKCS12, dump_certificate, dump_privatekey

cert_pem = dump_certificate(FILETYPE_PEM, certs .get_certificate())
key_pem = dump_privatekey(FILETYPE_PEM, certs .get_privatekey())