Python construct -.sizeof () for the construct depending on its parent

Question

This is a post about Python Construct Library

THE CODE

These are the definitions of my constructs:

from construct import *

AttributeHandleValuePair = "attribute_handle_value_pair" / Struct(
    "handle" / Int16ul,
    "value" / Bytes(this._.length - 2)
)

AttReadByTypeResponse = "read_by_type_response" / Struct(
    "length" / Int8ul,  # The size in bytes of each handle/value pair
    "attribute_data_list" / AttributeHandleValuePair[2]
)

PROBLEM

Attempting to execute the following command:

AttReadByTypeResponse.sizeof(dict(length=4, attribute_data_list=[dict(handle=1, value=2), dict(handle=3, value=4)])

I get the following error:

SizeofError: cannot calculate size, key not found in context
    sizeof -> read_by_type_response -> attribute_data_list -> attribute_handle_value_pair -> value

WHAT I FOUND

The size of the field valuefor each attribute_handle_value_pairis inferred from the field of lengthits parent. I think the method sizeof()tries to calculate the size first attribute_handle_value_pair, while the field length read_by_type_responseis still undefined, so it cannot calculate its size.

I tried changing the length of the field valueto a static value and it worked fine.

MY QUESTION

How can I calculate sizeof()for a construct that depends on its parent construct?

? , ?