Source Code Conventions

The guidelines below should be followed for any new code added to freud.

Naming Conventions

The following conventions should apply to Python, Cython, and C++ code.

  • Variable names use lower_case_with_underscores

  • Function and method names use lowerCaseWithNoUnderscores

  • Class names use CapWords


  • Spaces, not tabs, must be used for indentation

  • 4 spaces are required per level of indentation and continuation lines


Code in freud should follow PEP 8, as well as the following guidelines. Anything listed here takes precedence over PEP 8, but try to deviate as little as possible from PEP 8. When in doubt, follow these guidelines over PEP 8.

During continuous integration (CI), all Python and Cython code in freud is tested with flake8 to ensure PEP 8 compliance. It is strongly recommended to set up a pre-commit hook to ensure code is compliant before pushing to the repository:

flake8 --install-hook git
git config --bool flake8.strict true


  • All code should be contained in Cython files

  • Python .py files are reserved for module level docstrings and minor miscellaneous tasks for, e.g, backwards compatibility.

  • Semicolons should not be used to mark the end of lines in Python.

Documentation Comments

  • Documentation is generated using sphinx.

  • The documentation should be written according to the Google Python Style Guide.

  • A few specific notes:

    • The shapes of NumPy arrays should be documented as part of the type in the following manner:

      points ((:math:`N_{points}`, 3) :class:`numpy.ndarray`):
    • Constructors should be documented at the class level.

    • Class attributes (including properties) should be documented as class attributes within the class-level docstring.

    • Optional arguments should be documented as such within the type after the actual type, and the default value should be included within the description:

      box (:class:``, optional): Simulation box (Default value = None).
    • Properties that are settable should be documented the same way as optional arguments: Lx (float, settable): Length in x.

  • All docstrings should be contained within the Cython files.

  • If you copy an existing file as a template, make sure to modify the comments to reflect the new file.

  • Docstrings should demonstrate how to use the code with an example. Liberal addition of examples is encouraged.


C++ code should follow the result of running clang-format-6.0 with the style specified in the file .clang-format. Please refer to Clang Format 6 for details.

When in doubt, run clang-format -style=file FILE_WITH_YOUR_CODE in the top directory of the freud repository. If installing clang-format is not a viable option, the check-style step of continuous integration (CI) contains the information on the correctness of the style.


  • TBB sections should use lambdas, not functors (see this tutorial).

void someFunction(float some_var, float other_var)
    // code before parallel section
    parallel_for(blocked_range<size_t>(0, n), [=](const blocked_range<size_t>& r) {
        // do stuff

Documentation Comments

  • Add explanatory comments throughout your code.