How to use the impacket.structure.Structure function in impacket

raise Exception('Unsupported etype 0x%x' % cipher.enctype)

# 7.2.   GSS-API MIC Semantics
class GSSAPI_RC4:
    # 1.2.1. Per-message Tokens - MIC
    class MIC(Structure):
        structure = (
            ('TOK_ID','

)

class LSARPCCloseResponse(Structure):
    structure = (
        ('ContextHandle','20s'),
        ('ErrorCode','

# 2.2.10.1 USER_PROPERTIES
class USER_PROPERTIES(Structure):
    structure = (
        ('Reserved1','

('Unknown','12s=b""'),
        ('_Secret','_-Secret','self["Length"]'),
        ('Secret',':'),
        ('Remaining',':'),
    )

class LSA_SECRET(Structure):
    structure = (
        ('Version','

class SMB2Read_Response(Structure):
    structure = (
        ('StructureSize','

def fromString(self, data):
        Structure.fromString(self, data)
        if self['HostNameLength'] > 0:
            self['HostName'] = data[self['HostNameOffset']:][:self['HostNameLength']*2]

        if self['UserNameLength'] > 0:
            self['UserName'] = data[self['UserNameOffset']:][:self['UserNameLength']*2]

        if self['PasswordLength'] > 0:
            self['Password'] = data[self['PasswordOffset']:][:self['PasswordLength']*2]

        if self['AppNameLength'] > 0:
            self['AppName'] = data[self['AppNameOffset']:][:self['AppNameLength']*2]

        if self['ServerNameLength'] > 0:
            self['ServerName'] = data[self['ServerNameOffset']:][:self['ServerNameLength']*2]

        if self['CltIntNameLength'] > 0:

structure = (
        ('StructureSize','

class SRV_READ_HASH(Structure):
    structure = (
        ('HashType','

octetString = CountedOctetString()
        octetString['length'] = len(principal.realm)
        octetString['data'] = principal.realm
        self.realm = octetString
        self.components = []
        for c in principal.components:
            octetString = CountedOctetString()
            octetString['length'] = len(c)
            octetString['data'] = c
            self.components.append(octetString)

    def toPrincipal(self):
        return types.Principal(self.prettyPrint(), type=self.header['name_type'])

class Credential:
    class CredentialHeader(Structure):
        structure = (
            ('client',':', Principal),
            ('server',':', Principal),
            ('key',':', KeyBlock),
            ('time',':', Times),
            ('is_skey','B=0'),
            ('tktflags','!L=0'),
            ('num_address','!L=0'),
        )

    def __init__(self, data=None):
        self.addresses = ()
        self.authData = ()
        self.header = None
        self.ticket = None
        self.secondTicket = None

self.fromString(data)
        else:
            self.data = None

# 2.2.57 InstanceQualifierSet
class INSTANCE_QUALIFIER_SET(Structure):
    structure = (
        ('QualifierSet', ':', QUALIFIER_SET),
        ('InstancePropQualifierSet', ':', INSTANCE_PROP_QUALIFIER_SET),
    )

# 2.2.58 InstanceHeap
INSTANCE_HEAP = HEAP

# 2.2.53 InstanceType
class INSTANCE_TYPE(Structure):
    commonHdr = (
        ('CurrentClass', ':', CURRENT_CLASS_NO_METHODS),
        ('EncodingLength', ENCODING_LENGTH),
        ('InstanceFlags', INSTANCE_FLAGS),
        ('InstanceClassName', INSTANCE_CLASS_NAME),
        ('_NdTable_ValueTable', '_-NdTable_ValueTable',
         'self["CurrentClass"]["ClassPart"]["ClassHeader"]["NdTableValueTableLength"]'),
        ('NdTable_ValueTable',':'),
        ('InstanceQualifierSet', ':', INSTANCE_QUALIFIER_SET),
        ('InstanceHeap', ':', INSTANCE_HEAP),
    )

    def __init__(self, data = None, alignment = 0):
        Structure.__init__(self, data, alignment)
        self.structure = ()
        if data is not None: