31. Working with JSON APIs (parsing, validation)

Blockchain RPC responses typically arrive as JSON. After `json.loads`, validate shape before trusting values, since malformed or partial data is common.

python
import json

def parse_block(raw: str) -> dict:
    data = json.loads(raw)
    required = {"number", "hash", "transactions"}
    missing = required - data.keys()
    if missing:
        raise ValueError(f"missing fields: {missing}")
    return data

Hex-encoded quantities (e.g. `"0x1a"`) are common in RPC payloads; convert with `int(value, 16)`. Always guard against `KeyError`/`json.JSONDecodeError` when parsing external data rather than assuming well-formed input.

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