How to use the blspy.ExtendedPrivateKey function in blspy

ExtendedPrivateKey, ExtendedPublicKey, ChainCode)
from src.util.type_checking import strictdataclass, is_type_List, is_type_SpecificOptional
from src.types.sized_bytes import bytes32
from src.util.ints import uint32

pp = pprint.PrettyPrinter(indent=1, width=120, compact=True)

# TODO: Remove hack, this allows streaming these objects from binary
size_hints = {
    "PrivateKey": PrivateKey.PRIVATE_KEY_SIZE,
    "PublicKey": PublicKey.PUBLIC_KEY_SIZE,
    "Signature": Signature.SIGNATURE_SIZE,
    "InsecureSignature": InsecureSignature.SIGNATURE_SIZE,
    "PrependSignature": PrependSignature.SIGNATURE_SIZE,
    "ExtendedPublicKey": ExtendedPublicKey.EXTENDED_PUBLIC_KEY_SIZE,
    "ExtendedPrivateKey": ExtendedPrivateKey.EXTENDED_PRIVATE_KEY_SIZE,
    "ChainCode": ChainCode.CHAIN_CODE_KEY_SIZE
}
unhashable_types = [PrivateKey, PublicKey, Signature, PrependSignature, InsecureSignature,
                    ExtendedPublicKey, ExtendedPrivateKey, ChainCode]


def streamable(cls: Any):
    """
    This is a decorator for class definitions. It applies the strictdataclass decorator,
    which checks all types at construction. It also defines a simple serialization format,
    and adds parse, from bytes, stream, and __bytes__ methods.

    Serialization format:
    - Each field is serialized in order, by calling from_bytes/__bytes__.
    - For Lists, there is a 4 byte prefix for the list length.
    - For Optionals, there is a one byte prefix, 1 iff object is present, 0 iff not.