Python internals: easy

Opening your lesson

A short Python interview question often tests whether you can explain a surprising result and then repair the contract. Shared inner lists, late-bound loop variables and consumed iterators all fit in a few lines, but their effects can reach a much larger service.

This easy set asks for runnable functions on original inputs. State the ownership rule before implementing the fix. A deep copy changes nested ownership, a captured default preserves a loop value, and an iterator resumes from its current position. Frozen value objects need equality and hashing that agree. The checks accept any implementation with the required behavior. They don't award credit for repeating a definition without handling the supplied edge case.

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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