Cheat Sheet

Quick reference for current Xian contract development.

State Primitives

owner = Variable()
balances = Hash(default_value=0)
metadata = Hash()

foreign_owner = ForeignVariable(
    foreign_contract="currency",
    foreign_name="owner",
)

foreign_balances = ForeignHash(
    foreign_contract="currency",
    foreign_name="balances",
)

Events

TransferEvent = LogEvent(
    event="Transfer",
    params={
        "from": {"type": str, "idx": True},
        "to": {"type": str, "idx": True},
        "amount": {"type": (int, float, decimal)},
    },
)

Decorators

@construct
def seed():
    owner.set(ctx.caller)

@export
def transfer(to: str, amount: float):
    pass

def helper():
    pass

Export Signature Types

Allowed for exported arguments and exported return annotations:

str, int, float, bool, dict, list, Any
datetime.datetime, datetime.timedelta

Context

Name	Meaning
ctx.caller	immediate caller
ctx.signer	original transaction signer
ctx.this	current contract name
ctx.owner	current contract owner
ctx.entry	(contract, function) entry point

Environment Values

Name	Meaning
now	deterministic block time
block_num	current block height
block_hash	current block hash
chain_id	network id

Imports

import currency
import hashlib
import datetime
import random
import importlib
import crypto
import decimal

Do not use from x import y.

Read / Write Patterns

owner.set("alice")
current_owner = owner.get()

balances["alice"] = 100
balances["alice", "con_dex"] = 25

bal = balances["alice"]
allowance = balances["alice", "con_dex"]

Client-side direct inspection:

client.get_var("con_token", "balances", arguments=["alice"])
client.set_var("con_token", "balances", arguments=["alice"], value=500)

Common Assertions

assert amount > 0, "Amount must be positive"
assert balances[ctx.caller] >= amount, "Insufficient balance"
assert ctx.caller == owner.get(), "Only owner"
assert ctx.caller == ctx.signer, "Direct calls only"

Common Token Surface

@export
def transfer(amount: float, to: str):
    ...

@export
def approve(amount: float, to: str):
    ...

@export
def transfer_from(amount: float, to: str, main_account: str):
    ...

@export
def balance_of(address: str) -> float:
    ...

Disallowed Patterns

• classes
• nested functions
• try/except
• lambda
• async
• generators / yield
• stdlib imports
• names starting or ending with _