xian-tech-py 0.4.19

Python SDK for interacting with the Xian blockchain

xian-py

xian-py is the Python SDK for talking to Xian nodes from applications, workers, automation jobs, and operator tooling. It exposes a clean sync / async client surface over node RPCs, indexed BDS queries, and the CometBFT websocket, plus reusable projector primitives for building local read models.

The published PyPI package is xian-tech-py. The import package remains xian_py.

SDK Shape

flowchart LR
  App["Application or worker"] --> Sync["Xian sync client"]
  App --> Async["XianAsync client"]
  Sync --> RPC["Node RPC"]
  Async --> RPC
  Async --> WS["CometBFT websocket"]
  Sync --> BDS["Indexed BDS APIs"]
  Async --> BDS
  BDS --> Projector["EventProjector and cursors"]
  Wallet["Wallet"] --> Sync
  Wallet --> Async

Quick Start

Install the SDK:

uv add xian-tech-py

Read state and submit a transaction with the synchronous client:

import os

from xian_py import Wallet, Xian

wallet = Wallet(private_key=os.environ["XIAN_PRIVATE_KEY"])

with Xian("http://127.0.0.1:26657", wallet=wallet) as client:
    balance = client.token().balance_of(wallet.public_key)
    submission = client.token().transfer("bob", 5, mode="checktx")
    print(balance, submission.accepted)

Watch indexed events with the async client:

import asyncio

from xian_py import XianAsync


async def main() -> None:
    async with XianAsync("http://127.0.0.1:26657") as client:
        async for event in client.token().transfers().watch(after_id=0):
            print(event.id, event.data)


asyncio.run(main())

For low-latency delivery without BDS-backed cursoring, use raw live websocket events:

import asyncio

from xian_py import XianAsync


async def main() -> None:
    async with XianAsync("http://127.0.0.1:26657") as client:
        async for event in client.token().transfers().watch_live():
            print(event.tx_hash, event.data)


asyncio.run(main())

The SDK derives the websocket endpoint from the RPC URL by default (http://127.0.0.1:26657 → ws://127.0.0.1:26657/websocket). Override with WatcherConfig(websocket_url="ws://rpc-host:26657/websocket").

For visibility into transport retries, attach a callback to RetryPolicy(on_retry=...). The callback receives a typed RetryEvent with the operation kind, attempt number, next backoff delay, and exception.

Optional extras:

uv add "xian-tech-py[app]"   # FastAPI examples
uv add "xian-tech-py[eth]"   # Ethereum-style key helpers
uv add "xian-tech-py[hd]"    # HD-wallet derivation

SDK Cookbook

The examples below assume a running node at http://127.0.0.1:26657. Use xian-stack or xian-cli to start a local node, then pass the same RPC URL into the SDK.

Create or import a wallet:

import os

from xian_py import Wallet
from xian_py.wallet import HDWallet

# Generate a fresh Ed25519 account.
wallet = Wallet()
print(wallet.public_key)

# Restore an existing account from a hex private key.
wallet = Wallet(private_key=os.environ["XIAN_PRIVATE_KEY"])

# Optional HD-wallet derivation. Requires: uv add "xian-tech-py[hd]".
hd = HDWallet()
derived_wallet = hd.get_wallet([44, 734, 0, 0, 0])

# Browser/mobile wallet recovery compatibility. Also requires [hd].
wallet = Wallet.from_mnemonic_xian_v1(os.environ["XIAN_RECOVERY_PHRASE"])
second_account = Wallet.from_mnemonic_xian_v1(
    os.environ["XIAN_RECOVERY_PHRASE"], account_index=1
)

Inspect node and indexer health:

from xian_py import Xian

with Xian("http://127.0.0.1:26657") as client:
    status = client.get_node_status()
    bds = client.get_bds_status()
    print(status.network, status.latest_block_height, status.catching_up)
    print(bds.indexed_height, bds.height_lag, bds.alerts)

Read state, simulate a call, and retrieve contract source:

from xian_py import Xian

address = "bob"

with Xian("http://127.0.0.1:26657") as client:
    balance = client.token().balance_of(address)
    raw_balance = client.state_key("currency", "balances", address).get()
    simulated = client.contract("currency").simulate(
        "balance_of",
        address=address,
    )
    source = client.contract("currency").get_source()
    vm_ir = client.contract("currency").get_ir()
    print(balance, raw_balance, simulated["result"])

Estimate chi, submit a transaction, and wait for finality:

import os

from xian_py import Wallet, Xian

wallet = Wallet(private_key=os.environ["XIAN_PRIVATE_KEY"])

with Xian("http://127.0.0.1:26657", wallet=wallet) as client:
    estimate = client.estimate_chi(
        "currency",
        "transfer",
        {"to": "bob", "amount": 5},
    )
    submission = client.token().transfer(
        "bob",
        5,
        chi=estimate["estimated"],
        mode="checktx",
        wait_for_tx=True,
    )
    print(submission.tx_hash, submission.accepted, submission.finalized)
    if submission.receipt:
        print(submission.receipt.success)

Deploy a contract from source:

import os

from xian_py import Wallet, Xian

wallet = Wallet(private_key=os.environ["XIAN_PRIVATE_KEY"])
source = """
counter = Variable()

@construct
def seed():
    counter.set(0)

@export
def increment():
    counter.set(counter.get() + 1)
    return counter.get()
"""

with Xian("http://127.0.0.1:26657", wallet=wallet) as client:
    deployed = client.deploy_contract(
        "con_counter",
        source,
        mode="checktx",
        wait_for_tx=True,
    )
    result = client.contract("con_counter").send(
        "increment",
        mode="checktx",
        wait_for_tx=True,
    )
    print(deployed.tx_hash, result.tx_hash)

deploy_contract builds the Xian VM deployment artifacts locally before submitting. To submit artifacts produced by another toolchain, such as xian contract build-artifacts, call submit_contract(name, deployment_artifacts) directly.

Query BDS-backed history:

from xian_py import Xian

address = "bob"

with Xian("http://127.0.0.1:26657") as client:
    recent_blocks = client.list_blocks(limit=5)
    token_balances = client.get_token_balances(address, include_zero=False)
    currency_txs = client.list_txs_by_contract("currency", limit=20)
    transfer_events = client.list_events("currency", "Transfer", after_id=0)
    balance_history = client.get_state_history(f"currency.balances:{address}")
    print(
        len(recent_blocks),
        token_balances.total,
        len(currency_txs),
        len(transfer_events),
        len(balance_history),
    )

Use the async client in a service or worker:

import asyncio
import os

from xian_py import Wallet, XianAsync


async def main() -> None:
    wallet = Wallet(private_key=os.environ["XIAN_PRIVATE_KEY"])
    async with XianAsync("http://127.0.0.1:26657", wallet=wallet) as client:
        chain_id = await client.get_chain_id()
        balance = await client.token().balance_of(wallet.public_key)
        submission = await client.token().transfer(
            "bob",
            5,
            mode="checktx",
            wait_for_tx=True,
        )
        print(chain_id, balance, submission.tx_hash)


asyncio.run(main())

Build a resumable SQLite projection:

import asyncio
import sqlite3

from xian_py import (
    EventProjector,
    EventSource,
    SQLiteProjectionState,
    XianAsync,
    merged_event_payload,
)


async def main() -> None:
    connection = sqlite3.connect("projection.db")
    connection.row_factory = sqlite3.Row
    connection.execute(
        "CREATE TABLE IF NOT EXISTS transfers "
        "(event_id INTEGER PRIMARY KEY, tx_hash TEXT, amount TEXT)"
    )
    state = SQLiteProjectionState(connection)
    state.init_schema()

    source = EventSource("currency", "Transfer")

    async def apply_transfer(event, _hydrated):
        payload = merged_event_payload(event)
        connection.execute(
            "INSERT OR IGNORE INTO transfers VALUES (?, ?, ?)",
            (event.id, event.tx_hash, str(payload.get("amount"))),
        )
        state.set_int(source.key, event.id or 0)
        connection.commit()
        return True

    async with XianAsync("http://127.0.0.1:26657") as client:
        projector = EventProjector(
            client=client,
            event_sources=[source],
            get_cursor=lambda event_source: state.get_int(event_source.key),
            apply_event=apply_transfer,
        )
        await projector.sync_once()


asyncio.run(main())

Tune retries, transaction defaults, and watcher behavior:

from xian_py import (
    RetryEvent,
    RetryPolicy,
    SubmissionConfig,
    WatcherConfig,
    Xian,
    XianClientConfig,
)


def log_retry(event: RetryEvent) -> None:
    print(
        event.operation,
        event.attempt,
        event.max_attempts,
        event.next_delay_seconds,
        event.error,
    )


config = XianClientConfig(
    retry=RetryPolicy(max_attempts=5, on_retry=log_retry),
    submission=SubmissionConfig(mode="checktx", wait_for_tx=True),
    watcher=WatcherConfig(mode="auto", batch_limit=250),
)

with Xian("http://127.0.0.1:26657", config=config) as client:
    print(client.get_chain_id())

Talk to a shielded relayer:

from xian_py import ShieldedRelayerClient

with ShieldedRelayerClient("http://127.0.0.1:38480") as relayer:
    info = relayer.get_info()
    quote = relayer.get_quote(
        kind="shielded_command",
        contract="shielded_note_token",
        target_contract="currency",
    )
    print(info.available, quote.relayer_fee, quote.expires_at)

Principles

• One mental model, two clients. Sync and async clients stay aligned, so the same concepts work in scripts, services, and workers.
• Explicit transaction submission. Choose a broadcast mode (async, checktx, commit) deliberately. The SDK does not hide retry, blocking, or finality behavior.
• Plumbing, not policy. Read models and projector loops belong in application code. The SDK owns the repetitive plumbing (websocket delivery, catch-up cursors, raw CometBFT decoding, typed event conversion).
• Reference apps live alongside, not inside, the wheel. Examples demonstrate how to integrate Xian into Python systems but are not part of the published package.
• No node orchestration. Operator workflow and node lifecycle live in xian-cli and xian-stack.

Key Directories

• src/xian_py/ — clients, wallet helpers, transactions, models, projectors.
  • xian.py, xian_async.py — primary sync and async clients.
  • application_clients.py — thin helper clients (contract, token, events, state_key).
  • transaction.py, wallet.py, crypto.py — signing, building, and submitting transactions.
  • projectors.py — reusable polling, ordering, and checkpoint primitives.
  • models.py — typed transaction, event, block, and status models.
  • shielded_relayer.py — client for the private-submission relayer.
  • x402.py — native-Xian x402 exact-payment helpers.
• examples/ — service, worker, and reference-app examples built on the SDK (credits_ledger/, registry_approval/, workflow_backend/, x402_exact/, fastapi_service.py, event_worker.py, admin_job.py).
• tests/ — SDK transport, decoding, and integration-shape coverage.
• docs/ — compatibility notes and SDK backlog items.

Capabilities

• read current state via ABCI query paths and simulate readonly contract calls
• retrieve canonical contract source and Xian VM IR separately
• create, sign, and broadcast transactions with explicit async, checktx, and commit modes; wait for final receipts
• query indexed blocks, transactions, events, state history, and developer reward aggregates from BDS-backed nodes
• watch indexed events with websocket live delivery plus resumable BDS cursors
• watch raw live websocket events without BDS when low-latency delivery matters more than replayable cursors
• use thin helper clients for common patterns: contract, token, event, and state-key access
• sign, verify, settle, and retry native-Xian x402 exact-payment requests
• build SQLite-backed read models with the shared projector primitives, using CometBFT websocket wakeups and BDS cursor reconciliation

Event watching uses the CometBFT websocket directly and expects a BDS-enabled node for cursorable indexed catch-up and canonical event IDs. Use watch_live_events() or .watch_live() when you explicitly want websocket-only, non-resumable delivery.

Core API Layers

• Xian / XianAsync — primary sync and async clients
• client.contract(...), client.token(...), client.events(...), client.state_key(...) — thin helper clients for common patterns
• Typed models and error classes — predictable result handling instead of raw dictionaries
• EventProjector, EventSource, SQLiteProjectionState — reusable polling / ordering / checkpoint primitives for local projections
• Wallet — Ed25519 signing helper for Xian transactions

Typical Use Cases

• backend APIs that read state and submit transactions
• background workers that react to indexed events
• automation jobs that reconcile or administer contracts
• local projections that mirror chain activity into an application-owned SQLite read model
• operator or integration scripts that need a clean Python surface over node RPCs and indexed queries

Example Paths

• general SDK examples: examples/README.md
• credits-ledger reference app: examples/credits_ledger/README.md
• registry-approval reference app: examples/registry_approval/README.md
• workflow-backend reference app: examples/workflow_backend/README.md
• x402 exact-payment reference app: examples/x402_exact/README.md

Validation

uv sync --group dev
uv run ruff check .
uv run ruff format --check .
uv run pytest

Related Docs

• AGENTS.md — repo-specific guidance for AI agents and contributors
• docs/README.md — index of internal docs
• docs/ARCHITECTURE.md — major components and dependency direction
• docs/BACKLOG.md — open work and follow-ups
• docs/API_COMPATIBILITY.md — compatibility surface and stability guarantees
• docs/SDK_REVIEW_BACKLOG.md — SDK review queue