The OpShin Book
Introduction to the OpShin programming languages
Disclaimer: This book is still WIP, so expect incomplete or missing information.
Opshin is a pythonic language for writing smart contracts on the Cardano blockchain. The goal of Opshin is to reduce the barrier of entry in Smart Contract development on Cardano. Opshin is a strict subset of Python, this is means anyone who knows Python can get up to speed on Opshin pretty quickly.
On Cardano, funds are stored at addresses. An address can be controlled by a cryptographic key, the secret for unlocking it being only known to a specific user. The alternative is a Smart Contract - this is some encoded logic that controls unlocking funds from the address. In particular, this logic just validates that funds may be unlocked from the address based on how they are spent. For this reason, this kind of smart contract is often referred to as Spending Validator.
Other contracts also exist i.e. to validate minting of native tokens, withdrawal of stake rewards or certification of stake pools.
The following contract validates that the signature of a special user is present in a transaction. The signature is specified by a third party and attached to an UTxO sent to the contract. The receiver can then construct a transaction where they unlock the funds from the contract. The contract allows this when it is provided the signature of the receiver.
from opshin.prelude import *
def validator(datum: WithdrawDatum, redeemer: None, context: ScriptContext) -> None:
sig_present = False
for s in context.tx_info.signatories:
if datum.pubkeyhash == s:
sig_present = True
assert sig_present, "Required signature missing"
- 100% valid Python. Leverage the existing tool stack for Python, syntax highlighting, linting, debugging, unit-testing, property-based testing, verification
- Intuitive. Just like Python.
- Flexible. Imperative, functional, the way you want it.
- Efficient & Secure. Static type inference ensures strict typing and optimized code.
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