Foundry is a blazing fast testing environment for EVM smart contracts. Python is the leading programming language for quantitative analysis and data science. A lot of financial quant work gets modelled in Python and sometimes these models needs to be implemented in Solidity to be used in a protocol.

This template provides a reference implementation for creating foundry tests that compare solidity code to an implementation of the same code in Python. It does this by taking advantage of foundry ffi and foundry's inbuilt fuzz tooling. Being able to compare python code against solidity code for correctness and differential analysis helps improve the security and reliability of quantitative solidity development and helps understand the limits of the EVM when it comes to developing quantitative models to be used on the EVM.

Note: this template assumes some familiarity with foundry and forge, if you are not familiar refer to the amazing foundry docs

Example implementations:

• GDAs by FrankieIsLost
• SABR by Rysk.

1. Make sure you have foundry installed, if you do not then follow the instructions here

2. Make sure you have python3 installed, if you do not then follow the instructions here.

3. Make sure you have pipenv installed, if you do not then follow the instructions here

4. Run pipenv install to install python dependencies.

Note: you can use any python virtual environment that you are comfortable with, this template uses pipenv.

5. Run forge install to install foundry dependencies.

To run the example test Counter.t.sol do pipenv run forge test --ffi. This test fuzzes the function incrementByInput(i) in Counter.sol and compares the output against a python implementation of the same function which can be seen in python-scripts/counter.py. The test suite Counter.t.sol uses foundry ffi to run the python script alongside the foundry test. The example of its use can be seen in: testIncrementByInputFFIFuzz and ffiPy This allows for comparison between a python reference implementation of a function and a solidity function.

Alternatively, you can set up the repo and run the example using docker.

To build a local image by running docker build -t foundry-python-template.

docker run --platform linux/amd64 -d --name foundry template forge test --ffi

pipenv run forge test --ffi

When running the tests you must include the pipenv run and the --ffi in order to run the python-foundry differential fuzz tests.

Run pipenv install <package-name>

1. In the reference python script follow the instructions in parse_args() to add more variables. These can then be accessed in the main function via args.<var>

2. In the ffiPy function add in more elements to the inputs array making sure to include the tag and variable pair, also increase the array length of inputs to match the new array length. Instructions are provided in ffiPy

Change inputs[2] in the ffiPy function to represent the correct file path to the targeted script.