pypechain

Type-safe Python bindings for Ethereum smart contracts!

Used by

Features

Static Python bindings for ethereum smart contracts.

• Parses JSON ABIs to create typesafe web3.py contract instances.
• Functions have typesafe function parameters and return values.
• Functions have transparent exceptions that contains decoded error messages and more.
• Smart Contract internal types are exposed as dataclasses.
• Contract event interfaces are exposed as typesafe dataclasses.
• Helper functions to deploy a given contract.
• Helper functions for get_logs_typed and process_receipt_typed to return typesafe dataclass events.
• Helper functions for signing, transacting, and waiting for transaction receipts.

This project is a work-in-progress. All code is provided as is and without guarantee.

Install

pip install --upgrade pypechain

For development install instructions, see toplevel INSTALL.md

Packages 📦

Package Name	Version	Description
pypechain		Codegen python interfaces for web3.py contracts.
autoflake		Removes unused imports and unused variables
black		The uncompromising code formatter.
isort		A Python utility / library to sort Python imports.
jinja2		A very fast and expressive template engine.
web3		web3.py

Usage

Pypechain is primarily to be used via the CLI:

❯❯ pypechain -h

usage: pypechain [-h] [--output-dir OUTPUT_DIR] [--line-length LINE_LENGTH] abi_file_path

Generates class files for a given abi.

positional arguments:
  abi_file_path         Path to the abi JSON file or directory containing multiple JSON files.

options:
  -h, --help            show this help message and exit
  --output-dir OUTPUT_DIR
                        Path to the directory where files will be generated. Defaults to pypechain_types.
  --line-length LINE_LENGTH
                        Optional argument for the output file's maximum line length. Defaults to 80.

However, you can also run the main script directly from Python:

from pypechain import pypechain

abi_dir = "some/abi/dir"
output_dir = "some/output/dir"

pypechain(abi_dir, output_dir)

Examples

Pypechain generates a Python module from compiled Solidity code in ABI format. This enables access to typesafe contract, struct, and event objects, which greatly improves the developer experience.

Accessing contract balances

Using web3:

from web3 import Web3
web3 = Web3()
base_token_address = "0xSomeAddress"
user_address = "0xUserAddress"

# Contract construction takes an ABI filepath string
base_token_contract = web3.eth.contract(
    abi=base_contract_abi, address=web3.to_checksum_address(base_token_address)
)

# Arbitrary function arguments and names forces one to examine the ABI JSON to know the values & types
# Additionally, the types are not specified as Python types in the ABI
fn_args = [user_address]
fn_kwargs = {}

# HARD TO DISCOVER ALL FUNCTIONS AND THEIR ARGUMENTS
contract_function = base_token_contract.get_function_by_name("balanceOf")(*fn_args, **fn_kwargs)

# The function call also takes arbitrary args and kwargs
call_args = []
call_kwargs = {}

# UNTYPED RETURN VALUE!!
return_values: dict[str, Any] = contract_function.call(*call_args, **call_kwargs)

Using Pypechain generated objects:

    from web3 import Web3
    from pypechain_types import ERC20MintableContract

    web3 = Web3()
    base_token_address = "0xSomeAddress"
    user_address = "0xUserAddress"

    # Contracts include a factory function to initialize with your given web3 provider
    base_token_contract: ERC20MintableContract = ERC20MintableContract.deploy(w3=web3, signer=user_address)

    # balanceOf is a class function, enabling IDE tab-completion, intuitive inspection, typed inputs and typed outputs
    user_base_balance: int = base_token_contract.functions.balanceOf(user_address).call()

Understanding contracts

Solidity files can be difficult to read for native Python programmers that have little exposure to smart contract code.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ReturnTypes {

    struct SimpleStruct {
        uint intVal;
        string strVal;
    }

    struct InnerStruct {
        bool boolVal;
    }

    struct NestedStruct {
        uint intVal;
        string strVal;
        InnerStruct innerStruct;
    }

    function mixStructsAndPrimitives() public pure returns (SimpleStruct memory simpleStruct, NestedStruct memory, uint, string memory name, bool YesOrNo) {
        simpleStruct = SimpleStruct({
            intVal: 1,
            strVal: "You are number 1"
        });
        NestedStruct memory nestedStruct = NestedStruct({
            intVal: 2,
            strVal: "You are number 2",
            innerStruct: InnerStruct({boolVal: true})
        });

        return (simpleStruct, nestedStruct, 1, "ReturnTypesContract", false);
    }
}

Running pypechain on the compiled ABI from this contract produces code that is more intuitive for Python programmers.

... # imports


@dataclass
class SimpleStruct:
    """SimpleStruct struct."""
    intVal: int
    strVal: str


@dataclass
class InnerStruct:
    """InnerStruct struct."""
    boolVal: bool


@dataclass
class NestedStruct:
    """NestedStruct struct."""
    intVal: int
    strVal: str
    innerStruct: InnerStruct

class ReturnTypesMixStructsAndPrimitivesContractFunction(ContractFunction):
    """ContractFunction for the mixStructsAndPrimitives method."""

    class ReturnValues(NamedTuple):
        """The return named tuple for MixStructsAndPrimitives."""

        simpleStruct: SimpleStruct
        arg2: NestedStruct
        arg3: int
        name: str
        YesOrNo: bool

    def __call__(self) -> ReturnTypesMixStructsAndPrimitivesContractFunction:
        clone = super().__call__()
        self.kwargs = clone.kwargs
        self.args = clone.args
        return self

    def call(
        self,
        transaction: TxParams | None = None,
        block_identifier: BlockIdentifier = "latest",
        state_override: CallOverride | None = None,
        ccip_read_enabled: bool | None = None,
    ) -> ReturnValues:
        """returns ReturnValues."""
        # Define the expected return types from the smart contract call
        return_types = [SimpleStruct, NestedStruct, int, str, bool]
        # Call the function
        raw_values = super().call(transaction, block_identifier, state_override, ccip_read_enabled)
        return self.ReturnValues(*rename_returned_types(return_types, raw_values))


class ReturnTypesContractFunctions(ContractFunctions):
    """ContractFunctions for the ReturnTypes contract."""

    mixStructsAndPrimitives: ReturnTypesMixStructsAndPrimitivesContractFunction

    def __init__(
        self,
        abi: ABI,
        w3: "Web3",
        address: ChecksumAddress | None = None,
        decode_tuples: bool | None = False,
    ) -> None:
        super().__init__(abi, w3, address, decode_tuples)
        self.mixStructsAndPrimitives = ReturnTypesMixStructsAndPrimitivesContractFunction.factory(
            "mixStructsAndPrimitives",
            w3=w3,
            contract_abi=abi,
            address=address,
            decode_tuples=decode_tuples,
            function_identifier="mixStructsAndPrimitives",
        )


class ReturnTypesContract(Contract):
    """A web3.py Contract class for the ReturnTypes contract."""

    abi: ABI = returntypes_abi
    bytecode: bytes = HexBytes(returntypes_bytecode)

    def __init__(self, address: ChecksumAddress | None = None) -> None:
        try:
            # Initialize parent Contract class
            super().__init__(address=address)
            self.functions = ReturnTypesContractFunctions(returntypes_abi, self.w3, address)
        except FallbackNotFound:
            print("Fallback function not found. Continuing...")

    functions: ReturnTypesContractFunctions

    @classmethod
    def deploy(cls, w3: Web3, signer: ChecksumAddress) -> Self:
        """Deploys and instance of the contract.

        Parameters
        ----------
        w3 : Web3
            A web3 instance.
        signer : ChecksumAddress
            The address to deploy the contract from.

        Returns
        -------
        Self
            A deployed instance of the contract.
        """
        deployer = cls.factory(w3=w3)
        tx_hash = deployer.constructor().transact({"from": signer})
        tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
        deployed_contract = deployer(address=tx_receipt.contractAddress)  # type: ignore
        return deployed_contract

    @classmethod
    def factory(cls, w3: Web3, class_name: str | None = None, **kwargs: Any) -> Type[Self]:
        contract = super().factory(w3, class_name, **kwargs)
        contract.functions = ReturnTypesContractFunctions(returntypes_abi, w3, None)
        return contract

Tests

We use pytest in our pypechain tests. Pytest, when ran locally, automatically compiles Solidity using Foundry, as well as running pypechain on the output abis.

If you run into issues during pytest, run make clean; make build-test to rebuild all solidity and pypechain types in tests.

We also use pytest-snapshot for some tests to ensure rendered files are as expected. If any changes are made to rendering that results in failures in snapshots, run pytest --snapshot-update, ensure the generated files in snapshots/ are as expected, and commit the new snapshots in snapshots/ as part of the update.

TODO also add in tests compiled via solc. See conftest.py for more information.