AsyncSRC20EventWatcher

Asynchronous SRC20 event watcher class

Polling-based SRC20 event watcher that runs as an asyncio.Task.

Typically created via async_watch_src20_events() or async_watch_src20_events_with_key() rather than instantiated directly.

Constructor

class AsyncSRC20EventWatcher:
    def __init__(
        self,
        w3: AsyncWeb3,
        aes_key: Bytes32,
        *,
        token_address: ChecksumAddress | None = None,
        on_transfer: AsyncTransferCallback | TransferCallback | None = None,
        on_approval: AsyncApprovalCallback | ApprovalCallback | None = None,
        on_error: AsyncErrorCallback | ErrorCallback | None = None,
        poll_interval: float = 2.0,
        from_block: int | str = "latest",
    ) -> None

Parameters

Parameter	Type	Default	Description
w3	AsyncWeb3		Async Web3 instance
aes_key	Bytes32		32-byte AES-256 viewing key
token_address	ChecksumAddress | None	None	SRC20 contract to filter (None = all tokens)
on_transfer	Callback	None	Async or sync callback for Transfer events
on_approval	Callback	None	Async or sync callback for Approval events
on_error	Callback	None	Async or sync callback for errors
poll_interval	float	2.0	Seconds between polls
from_block	int | "latest"	"latest"	Starting block

Methods

Method	Description
await start()	Start the async polling task
await stop()	Cancel the task and wait for cleanup
is_running	Property — True if task is active

Async Context Manager

async with AsyncSRC20EventWatcher(w3, key, on_transfer=cb) as watcher:
    await asyncio.sleep(60)
# Automatically stopped

Notes

• Callbacks can be sync or async — the watcher detects and awaits coroutines automatically

• CancelledError is suppressed during shutdown

• If on_error is not provided, errors are logged at DEBUG level

See Also

• SRC20EventWatcher — Sync variant

• watch_src20_events — Factory with auto key fetch

• watch_src20_events_with_key — Factory with explicit key

• DecryptedTransferLog — Transfer callback data

• DecryptedApprovalLog — Approval callback data