System Dependencies

Populus depends on the following system dependencies.

  • Solidity : For contract compilation
  • Go Ethereum: For running test chains and contract deployment.

In addition, populus needs some system dependencies to be able to install the PyEthereum library.

Debian, Ubuntu, Mint

sudo apt-get install libssl-dev

Fedora, CentOS, RedHat

sudo yum install openssl-devel


brew install pkg-config libffi autoconf automake libtool openssl


Populus can be installed using pip as follows.

$ pip install populus

By default populus will use standard library tools for io operations like threading and subprocesses. Populus can be configured to instead use gevent. To install with gevent support:

$ pip install populus[gevent]

To enable gevent set the environment variable THREADING_BACKEND=gevent.

Installation from source can be done from the root of the project with the following command.

$ python setup.py install

Initializing a new project

Populus can initialize your project using the $ populus init command.

$ populus init
Wrote default populus configuration to `./populus.json`.
Created Directory: ./contracts
Created Example Contract: ./contracts/Greeter.sol
Created Directory: ./tests
Created Example Tests: ./tests/test_greeter.py

Your project will now have a ./contracts directory with a single Solidity source file in it named Greeter.sol, as well as a ./tests directory with a single test file named test_greeter.py.

Compiling your contracts

Before you compile our project, lets take a look at the Greeter contract that is generated as part of the project initialization.

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;

Greeter is simple contract that is initialized with a default greeting of the string 'Hello'. It exposes the greet function which returns whatever string is set as the greeting, as well as a setGreeting function which allows the greeting to be changed.

You can now compile the contract using $ populus compile

$ populus compile
============ Compiling ==============
> Loading source files from: ./contracts

> Found 1 contract source files
- contracts/Greeter.sol

> Compiled 1 contracts
- Greeter

> Wrote compiled assets to: ./build/contracts.json

Testing your contract

Now that you have a basic contract you’ll want to test that it behaves as expected. The project should already have a test module named test_greeter.py located in the ./tests directory that looks like the following.

def test_greeter(chain):
    greeter, _ = chain.provider.get_or_deploy_contract('Greeter')

    greeting = greeter.call().greet()
    assert greeting == 'Hello'

def test_custom_greeting(chain):
    greeter, _ = chain.provider.get_or_deploy_contract('Greeter')

    set_txn_hash = greeter.transact().setGreeting('Guten Tag')

    greeting = greeter.call().greet()
    assert greeting == 'Guten Tag'

You should see two tests, one that tests the default greeting, and one that tests that we can set a custom greeting. You can run tests using the py.test command line utility which was installed when you installed populus.

$ py.test tests/
collected 2 items

tests/test_greeter.py::test_greeter PASSED
tests/test_greeter.py::test_custom_greeting PASSED

You should see something akin to the output above with three passing tests.

Setup for development and contribution

In order to configure the project locally and get the whole test suite passing, you’ll need to make sure you’re using the proper version of the solc compiler. Follow these steps to install all the dependencies:

Virtual environment

If you don’t already have it, go ahead and install virtualenv with pip install virtualenv. You can then create and activate your Populus environment with the following commands:

$ cd populus
$ virtualenv populus
$ source populus/bin/activate

This allows you to install the specific versions of the Populus dependencies without conflicting with global installations you may already have on your machine.

Install dependencies

Now, run the following commands to install all the dependencies specified in the project except for solc:

$ pip install -r requirements-dev.txt
$ pip install -r requirements-docs.txt
$ pip install -r requirements-gevent.txt
$ pip install -e .

Install Solidity

Here’s where the fun begins: you’ll have to build Solidity from source, and it specifically needs to be the release_0.4.8 branch. Here’s how to do that:

First, clone the repository and switch to the proper branch:

$ git clone --recursive https://github.com/ethereum/solidity.git
$ cd solidity
$ git checkout release_0.4.8

If you’re on a Mac, you may need to accept the Xcode license as well. Make sure you have the latest version installed, and if you run into errors, try the following:

$ sudo xcodebuild -license accept

If you’re on Windows, make sure you have Git, CMake, and Visual Studio 2015.

Now, install all the external dependencies. For Mac:

$ ./scripts/install_deps.sh

Or, for Windows:

$ scripts\install_deps.bat

Finally, go ahead and build Solidity. For Mac:

$ mkdir build
$ cd build
$ cmake .. && make

Or, for Windows:

$ mkdir build
$ cd build
$ cmake -G "Visual Studio 14 2015 Win64" ..

The following command will also work for Windows:

$ cmake --build . --config RelWithDebInfo


This should have installed everything you need, but let’s be sure. First, try running:

$ which solc

If you didn’t see any output, you’ll need to move the solc executable file into the directory specified in your PATH, or add an accurate PATH in your bash profile. If you can’t find the file, you may need to run:

$ npm install -g solc

This should install the executable wherever your Node packages live.

Once you see output from the which solc command (and you’re in the Populus directory with the virtualenv activated), you’re ready to run the tests.

$ py.test tests/

At this point, all your tests should pass. If they don’t, you’re probably missing a dependency somewhere. Just retrace your steps and you’ll figure it out.