eopsin

> You are building what you want. Why not also build how you want?

This is an implementation of smart contracts for Cardano which are written in a strict subset of valid Python. The general philosophy of this project is to write a compiler that ensure the following:

If the program compiles then:

1. it is a valid Python program
2. the output running it with python is the same as running it on-chain.

Why eopsin?

• 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

Getting Started

Eopsin Pioneer Program

Check out the eopsin-pioneer-program for a host of educational example contracts, test cases and off-chain code.

Example repository

Check out the eopsin-example repository for a quick start in setting up a development environment and compiling some sample contracts yourself.

You can replace the contracts in your local copy of the repository with code from the examples section here to start exploring different contracts.

Developer Community and Questions

This repository contains a discussions page. Feel free to open up a new discussion with questions regarding development using eopsin and using certain features. Others may be able to help you and will also benefit from the previously shared questions.

Check out the community here

You can also chat with other developers in the welcoming discord community of OpShin

Installation

Install Python 3.8. Then run

python3.8 -m pip install eopsin-lang

Writing a Smart Contract

A short non-complete introduction in starting to write smart contracts follows.

1. Make sure you understand EUTxOs, Addresses, Validators etc on Cardano. There is a wonderful crashcourse by @KtorZ. The contract will work on these concepts
2. Make sure you understand python. Eopsin works like python and uses python. There are tons of tutorials for python, choose what suits you best.
3. Make sure your contract is valid python and the types check out. Write simple contracts first and run them using eopsin eval to get a feeling for how they work.
4. Make sure your contract is valid eopsin code. Run eopsin compile and look at the compiler erros for guidance along what works and doesn't work and why.
5. Dig into the examples to understand common patterns. Check out the prelude for understanding how the Script Context is structured and how complex datums are defined.
6. Check out the sample repository to find a sample setup for developing your own contract.

In summary, a smart contract in eopsin is defined by the function validator in your contract file. The function validates that a specific value can be spent, minted, burned, withdrawn etc, depending on where it is invoked/used as a credential. If the function fails (i.e. raises an error of any kind such as a KeyError or AssertionError) the validation is denied, and the funds can not be spent, minted, burned etc.

> There is a subtle difference here in comparison to most other Smart Contract languages. > In eopsin a validator may return anything (in particular also False) - as long as it does not fail, the execution is considered valid. > This is more similar to how contracts in Solidity always pass, unless they run out of gas or hit an error. > So make sure to assert what you want to ensure to hold for validation!

A simple contract called the "Gift Contract" verifies that only specific wallets can withdraw money. They are authenticated by a signature. If you don't understand what a pubkeyhash is and how this validates anything, check out this gentle introduction into Cardanos EUTxO. Also see the tutorial by pycardano for explanations on what each of the parameters to the validator means and how to build transactions with the contract.

from eopsin.prelude import *

@dataclass()
class CancelDatum(PlutusData):
    pubkeyhash: bytes


def validator(datum: CancelDatum, 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"

All contracts written in eopsin are 100% valid python. Minting policies expect only a redeemer and script context as argument. Check out the Architecture guide for details on how to write double functioning contracts. The examples folder contains more examples. Also check out the eopsin-pioneer-program and eopsin-example repo.

Compiling

Write your program in python. You may start with the content of examples. Arguments to scripts are passed in as Plutus Data objects in JSON notation.

You can run any of the following commands

# Evaluate script in Python - this can be used to make sure there are no obvious errors
eopsin eval examples/smart_contracts/assert_sum.py "{\"int\": 4}" "{\"int\": 38}" "{\"constructor\": 0, \"fields\": []}"

# Compile script to 'uplc', the Cardano Smart Contract assembly
eopsin compile examples/smart_contracts/assert_sum.py

Deploying

The deploy process generates all artifacts required for usage with common libraries like pycardano, lucid and the cardano-cli.

# Automatically generate all artifacts needed for using this contract
eopsin build examples/smart_contracts/assert_sum.py

See the tutorial by pycardano for explanations how to build transactions with eopsin contracts.

The small print

Not every valid python program is a valid smart contract. Not all language features of python will or can be supported. The reasons are mainly of practical nature (i.e. we can't infer types when functions like eval are allowed). Specifically, only a pure subset of python is allowed. Further, only immutable objects may be generated.

For your program to be accepted, make sure to only make use of language constructs supported by the compiler. You will be notified of which constructs are not supported when trying to compile.

Name

> Eopsin (Korean: 업신; Hanja: 業神) is the goddess of the storage and wealth in Korean mythology and shamanism. > [...] Eopsin was believed to be a pitch-black snake that had ears. [1]

Since this project tries to merge Python (a large serpent) and Pluto/Plutus (Greek wealth gods), the name appears fitting.

The name is pronounced op-shin.

Contributing

Architecture

This program consists of a few independent components:

1. An aggressive static type inferencer
2. Rewriting tools to simplify complex python expressions
3. A compiler from a subset of python into UPLC

Debugging artefacts

For debugging purposes, you can also run

# Compile script to 'uplc', and evaluate the script in UPLC (for debugging purposes)
python3 -m eopsin eval_uplc examples/smart_contracts/assert_sum.py "{\"int\": 4}" "{\"int\": 38}" "{\"constructor\": 0, \"fields\": []}"

# Compile script to 'pluto', an intermediate language (for debugging purposes)
python3 -m eopsin compile_pluto examples/smart_contracts/assert_sum.py

Sponsoring

You can sponsor the development of eopsin through GitHub or Teiki or just by sending ADA. Drop me a message on social media and let me know what it is for.

• Teiki Stake your ada to support OpShin at Teiki
• GitHub Sponsor the developers of this project through the button "Sponsor" next to them
• ADA Donation in ADA can be submitted to $opshin or addr1qyz3vgd5xxevjy2rvqevz9n7n7dney8n6hqggp23479fm6vwpj9clsvsf85cd4xc59zjztr5zwpummwckmzr2myjwjns74lhmr.

Supporters