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.
Integration with pytest, flake8, sphinx, and hypothesis.
Type annotations support.
Colorless: annotate only what you want. Hence, easy integration into an existing project.
Colorful: syntax highlighting for every piece of code in every command.
Memory leaks detection: deal makes sure that pure functions don’t leave unexpected objects in the memory.
DRY: test discovery, error messages generation.
Partial execution: linter executes contracts to statically check possible values.
Formal verification: prove that your code works for all input (or find out when it doesn’t).
Zero-dependency runtime: there are some dependencies for analysis tools, but nothing of it is required on the production.
Fast: each code change is benchmarked and profiled.
Reliable: the library has 100% test coverage, partially verified, and runs on production by multiple companies since 2018.
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:
python3 -m deal lintor
flake8to statically check errors.
python3 -m deal testor
pytestto generate and run tests.
Just use the function in the project and check errors in runtime.
Read more in the documentation.
python3 -m pip install --user 'deal[all]'
Contributions are welcome! A few ideas what you can contribute:
Add new checks for the linter.
Add more tests.
Found a bug? Fix it!
Made an article about deal? Great! Let’s add it into the
Don’t have time to code? No worries! Just tell your friends and subscribers about the project. More users -> more contributors -> more cool features.
To run tests locally, all you need is task. Run
task all to run all code formatters, linters, and tests.
Thank you :heart: