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A Python implementation of web3.js

  • Python 3.5+ support

Read more in the documentation on ReadTheDocs. View the change log on Github.


import json
import web3

from web3 import Web3, HTTPProvider, TestRPCProvider
from solc import compile_source
from web3.contract import ConciseContract

# Solidity source code
contract_source_code = '''
pragma solidity ^0.4.0;

contract Greeter {
    string public greeting;

    function Greeter() {
        greeting = 'Hello';

    function setGreeting(string _greeting) public {
        greeting = _greeting;

    function greet() constant returns (string) {
        return greeting;

compiled_sol = compile_source(contract_source_code) # Compiled source code
contract_interface = compiled_sol['<stdin>:Greeter']

# instance
w3 = Web3(TestRPCProvider())

# Instantiate and deploy contract
contract = w3.eth.contract(abi=contract_interface['abi'], bytecode=contract_interface['bin'])

# Get transaction hash from deployed contract
tx_hash = contract.deploy(transaction={'from': w3.eth.accounts[0], 'gas': 410000})

# Get tx receipt to get contract address
tx_receipt = w3.eth.getTransactionReceipt(tx_hash)
contract_address = tx_receipt['contractAddress']

# Contract instance in concise mode
contract_instance = w3.eth.contract(contract_interface['abi'], contract_address, ContractFactoryClass=ConciseContract)

# Getters + Setters for web3.eth.contract object
print('Contract value: {}'.format(contract_instance.greet()))
contract_instance.setGreeting('Nihao', transact={'from': w3.eth.accounts[0]})
print('Setting value to: Nihao')
print('Contract value: {}'.format(contract_instance.greet()))

Developer setup

If you would like to hack on, set up your dev environment with:

sudo apt-get install libssl-dev libffi-dev autoconf automake libtool
# ^ This is for Debian-like systems. TODO: Add more platforms

sudo pacman -Sy libsecp256k1
# ^ This is for ArchLinux system

git clone
virtualenv venv
. venv/bin/activate
pip install -r requirements-dev.txt
pip install -e .

For different environments, you can set up multiple virtualenvs, like:

Python 3

virtualenv -p python3 venvpy3
. venvpy3/bin/activate
pip install -r requirements-dev.txt
pip install -e .[tester]


virtualenv venvdocs
. venvdocs/bin/activate
pip install -r requirements-docs.txt
pip install -e .

Using Docker

If you would like to develop and test inside a Docker environment, use the sandbox container provided in the docker-compose.yml file.

To start up the test environment, run:

docker-compose up -d

This will build a Docker container set up with an environment to run the Python test code.

Note: This container does not have ``go-ethereum`` installed, so you cannot run the go-ethereum test suite.

To run the Python tests from your local machine:

docker-compose exec sandbox bash -c 'pytest -n 4 -f -k "not goethereum"'

You can run arbitrary commands inside the Docker container by using the bash -c prefix.

docker-compose exec sandbox bash -c ''

Or, if you would like to just open a session to the container, run:

docker-compose exec sandbox bash

Testing Setup

During development, you might like to have tests run on every file save.

Show flake8 errors on file change:

# Test flake8
when-changed -v -s -r -1 web3/ tests/ ens/ -c "clear; flake8 web3 tests ens && echo 'flake8 success' || echo 'error'"

You can use pytest-watch, running one for every Python environment:

pip install pytest-watch

cd venv
ptw --onfail "notify-send -t 5000 'Test failure ⚠⚠⚠⚠⚠' 'python 3 test on failed'" ../tests ../web3

#in a new console
cd venvpy2
ptw --onfail "notify-send -t 5000 'Test failure ⚠⚠⚠⚠⚠' 'python 2 test on failed'" ../tests ../web3

Or, you can run multi-process tests in one command, but without color:

# in the project root:
py.test --numprocesses=4 --looponfail --maxfail=1
# the same thing, succinctly:
pytest -n 4 -f --maxfail=1

Release setup

For Debian-like systems:

apt install pandoc

To release a new version:

make release bump=$$VERSION_PART_TO_BUMP$$

How to bumpversion

The version format for this repo is {major}.{minor}.{patch} for stable, and {major}.{minor}.{patch}-{stage}.{devnum} for unstable (stage can be alpha or beta).

To issue the next version in line, specify which part to bump, like make release bump=minor or make release bump=devnum.

If you are in a beta version, make release bump=stage will switch to a stable.

To issue an unstable version when the current version is stable, specify the new version explicitly, like make release bump="--new-version 4.0.0-alpha.1 devnum"

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