Design and internals job test

Opening your lesson

This second original job-test simulation shifts the emphasis to language behavior and small domain designs. Eight tasks share one clock. A precise invariant will save more time than a large abstraction that you cannot finish checking.

You work with nested copying, closures, value objects, ownership, constrained allocation, guarded state and scheduling boundaries. The records are new, while the underlying techniques come from earlier units. There is no official certification claim and no assumption that a short function represents a whole production system. Use the smallest design that expresses the stated contract, then test a boundary before moving on. Duplicate records, equal choices and exact limits appear deliberately because those cases reveal whether the model is complete.

import json

def process_payload(payload: str) -> str:
    data = json.loads(payload)
    import copy
    original = data['rows']
    cloned = copy.deepcopy(original)
    if cloned:
        cloned[0].append(data['value'])
    return json.dumps([original,cloned],separators=(',',':'))

A shallow outer copy still shares inner lists; change only the first copied row. Copying only the outer list preserves references to its inner lists. The append must affect a new inner object. The deep copy visits the nested structure and costs space proportional to the copied values.

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