47. Parsing and validating on-chain-style event logs

Event logs from a chain indexer often arrive as a list of dicts with fields like `event`, `args`, and `blockNumber`. Filtering, grouping, and aggregating these is a common real-world Python task.

python
events = [
    {"event": "Transfer", "args": {"from": "0xa", "to": "0xb", "value": 10}, "blockNumber": 100},
    {"event": "Approval", "args": {"owner": "0xa", "spender": "0xc"}, "blockNumber": 101},
]

transfers = [e for e in events if e["event"] == "Transfer"]
total_value = sum(e["args"]["value"] for e in transfers)

from collections import defaultdict
by_block = defaultdict(list)
for e in events:
    by_block[e["blockNumber"]].append(e)

Defensive code checks `e.get("args", {}).get("value")` when fields might be absent, avoiding `KeyError` crashes on unexpected log shapes.

Check your understanding