Deal

Deal

Build Status PyPI version Development Status

A Python library for design by contract (DbC) and checking values, exceptions, and side-effects. In a nutshell, deal empowers you to write bug-free code. By adding a few decorators to your code, you get for free tests, static analysis, formal verification, and much more. Read intro to get started.

Features

Deal in 30 seconds

# the result is always non-negative
@deal.post(lambda result: result >= 0)
# the function has no side-effects
@deal.pure
def count(items: List[str], item: str) -> int:
    return items.count(item)

# generate test function
test_count = deal.cases(count)

Now we can:

  • Run python3 -m deal lint or flake8 to statically check errors.

  • Run python3 -m deal test or pytest to generate and run tests.

  • Just use the function in the project and check errors in runtime.

Read more in the documentation.

Installation

python3 -m pip install --user deal

Contributing

Contributions are welcome! A few ideas what you can contribute:

  • Add new checks for the linter.

  • Improve documentation.

  • Add more tests.

  • Improve performance.

  • Found a bug? Fix it!

  • Made an article about deal? Great! Let’s add it into the README.md.

  • Don’t have time to code? No worries! Just tell your friends and subscribers about the project. More users -> more contributors -> more cool features.

Thank you :heart:

Writing contracts