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Lint contracts defined with icontract library.

Project description


Continuous integration Test coverage Documentation status PyPI - version PyPI - Python Version

pyicontract-lint lints contracts in Python code defined with icontract library.

The following checks are performed:



File should be read and decoded correctly.


A preconditions expects a subset of function’s arguments.


A snapshot expects at most an argument element of the function’s arguments.


If a snapshot is defined on a function, a postcondition must be defined as well.


A capture function must be defined in the contract.


A postcondition expects a subset of function’s arguments.


If a function returns None, a postcondition should not expect result as argument.


If a postcondition expects result argument, the function should not expect it.


If a postcondition expects OLD argument, the function should not expect it.


An invariant should only expect self argument.


A condition must be defined in the contract.


File must be valid Python code.



Pyicontract-lint parses the code and tries to infer the imported modules and functions using astroid library. Hence you need to make sure that imported modules are on your PYTHONPATH before you invoke pyicontract-lint.

Once you set up the environment, invoke pyicontract-lint with a list of positional arguments as paths:

pyicontract-lint \
    /path/to/some/directory/ \

You can also invoke it on directories. Pyicontract-lint will recursively search for *.py files (including the subdirectories) and verify the files:

pyicontract-lint \

By default, pyicontract-lint outputs the errors in a verbose, human-readable format. If you prefer JSON, supply it --format argument:

pyicontract-lint \
    --format json \

If one or more checks fail, the return code will be non-zero. You can specify --dont_panic argument if you want to have a zero return code even though one or more checks failed:

pyicontract-lint \
    --dont_panic \

To disable any pyicontract-lint checks on a file, add # pyicontract-lint: disabled on a separate line to the file. This is useful when you recursively lint files in a directory and want to exclude certain files.

Module icontract_lint

The API is provided in the icontract_lint module if you want to use pycontract-lint programmatically.

The main points of entry in icontract_line module are:

  • check_file(...): lint a single file,

  • check_recursively(...): lint a directory and

  • check_paths(...): lint files and directories.

The output is produced by functions output_verbose(...) and output_json(...).

Here is an example code that lints a list of given paths and produces a verbose output:

import pathlib
import sys

import icontract_lint

errors = icontract_lint.check_paths(paths=[

output_verbose(errors=errors, stream=sys.stdout)

The full documentation of the module is available on readthedocs.


  • Install pyicontract-lint with pip:

pip3 install pyicontract-lint


  • Check out the repository.

  • In the repository root, create the virtual environment:

python3 -m venv venv3
  • Activate the virtual environment:

source venv3/bin/activate
  • Install the development dependencies:

pip3 install -e .[dev]
  • We use tox for testing and packaging the distribution. Run:

  • We also provide a set of pre-commit checks that lint and check code for formatting. Run them locally from an activated virtual environment with development dependencies:

  • The pre-commit script can also automatically format the code:

./  --overwrite


We follow Semantic Versioning. The version X.Y.Z indicates:

  • X is the major version (backward-incompatible),

  • Y is the minor version (backward-compatible), and

  • Z is the patch version (backward-compatible bug fix).

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