csr_attributes.py

from asn1crypto.csr import CertificationRequest

cr = CertificationRequest.load(der_bytes)
attrs = cr['certification_request_info']['attributes']
print(attrs.native)

notes.md

The fields are defined at https://github.com/wbond/asn1crypto/blob/master/asn1crypto/csr.py. Depending on your needs, you could duplicate the definitions with OID and spec data for your custom extensions.

That said, the code above doesn't actually do any validation of the CSR. That should be done before accessing the information.