Python script to check ROOT SSL Certificate

Question

I want to write a script that can verify a root CA certificate from its subordinate CA. Currently, I can only return the lowest level certificate. (For example, if you view the certification path for this web page, the script would return the certificate issued by R3, but I need to get the ISRG Root X1.)

Some of the code I'm using to pull a certificate from a hostname is as follows:

'''

def get_certificate(hostname, port):
hostname_idna = idna.encode(hostname)
sock = socket()

sock.connect((hostname, port))
peername = sock.getpeername()
ctx = SSL.Context(SSL.SSLv23_METHOD) # most compatible
ctx.check_hostname = False
ctx.verify_mode = SSL.VERIFY_NONE

sock_ssl = SSL.Connection(ctx, sock)
sock_ssl.set_connect_state()
sock_ssl.set_tlsext_host_name(hostname_idna)
sock_ssl.do_handshake()
cert = sock_ssl.get_peer_certificate()
crypto_cert = cert.to_cryptography()
sock_ssl.close()
sock.close()

return HostInfo(cert=crypto_cert, peername=peername, hostname=hostname)

def get_common_name(cert):
try:
    names = cert.subject.get_attributes_for_oid(NameOID.COMMON_NAME)
    return names[0].value
except x509.ExtensionNotFound:
    return None

def get_issuer(cert):
try:
    names = cert.issuer.get_attributes_for_oid(NameOID.COMMON_NAME)
    return names[0].value
except x509.ExtensionNotFound:
    return None

'''

I'm not sure how to climb the chain of authority to find the ROOT CA from its subordinate levels. Does anyone know how to return the root/tier 1 CA from its tier 2 or 3 certs?