Xian Documentation

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Smart Contracts ​

Xian smart contracts are written in Python, but not in unrestricted CPython. They run inside a deterministic sandbox with a small, explicit language surface, persistent state primitives, and stamp metering.

What Makes Xian Contracts Different ​

  • Python syntax, chain-safe semantics: contracts look like normal Python modules, but only a restricted subset is allowed.
  • Deterministic execution: the runtime rejects language features that would make validator results diverge.
  • Persistent state primitives: Variable, Hash, ForeignVariable, ForeignHash, and LogEvent are the storage/event building blocks.
  • Metered execution: compute and storage both consume stamps.
  • Explicit imports: contracts can import deployed contracts and a small runtime stdlib, not arbitrary Python modules.

Contract Anatomy ​

Every contract is a single module with module-level declarations, an optional constructor, and one or more exported functions:

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

@construct
def seed():
    owner.set(ctx.caller)
    balances[ctx.caller] = 1_000_000

@export
def transfer(to: str, amount: float):
    assert amount > 0, "Amount must be positive"
    assert balances[ctx.caller] >= amount, "Insufficient balance"
    balances[ctx.caller] -= amount
    balances[to] += amount

Current Rules To Remember ​

  • module-level state declarations and imports are allowed
  • at least one @export function is required
  • exported function arguments must be annotated
  • exported function return annotations are allowed, but only with the same whitelisted types accepted for arguments
  • names starting or ending with _ are rejected
  • classes, nested functions, try/except, lambda, async, yield, and from x import y are rejected