Code Style Guide

This section defines a style guide which should be followed by all code that is written in Drake. Being consistent with this style will make the code easier to read, debug, and maintain. To ensure your code is style compliant, consider using tools for complying with coding style.

See also the brief Code Review Checklist, where a list of the most frequent problems are collected.

Note: Many of the files in the repository were written before this style guide, or did not follow it precisely. If you find style errors, go ahead and change it and submit a pull request.

C++ Style

The Drake C++ style guide (which is derived from the Google C++ style guide) can be found on its own page. Its source lives in the styleguide repository.

Python Style

Drake strictly follows PEP 8 – Style Guide for Python Code except for the specific clarifications, exceptions, and additional rules noted below. Since PEP 8 incorporates PEP 257 – Docstring Conventions, Drake follows its recommendations as well.

Drake also follows the RobotLocomotion fork of the Google Python Style Guide. Please refer to that page for the sections that are adhered to, and the relevant exceptions.

See tools for complying with coding style for details about the automated style checks.

Clarifications

  • External, third-party, and auto-generated source files are not to be checked for style.
  • Always prefer long, human-readable variable/method/class names to short acronyms.

Exceptions

  • Lines containing a long URL may be longer than 80 columns if necessary to avoid splitting the URL.

Additional Rules

  • When importing in-tree modules, always use absolute import paths; explicit relative import paths are disallowed. See the PEP 8 discussion of imports for more detail.
  • Sometimes __init__.py files are necessary, for Python’s import mechanism; these files should be non-empty (via a copyright notice, for example). Rationale: 0-byte files can be mistakenly perceived as the result of some error or accident.
  • When using the logging module, avoid its lazy-formatting syntax. Rationale: exceptions raised in lazy formatting get printed to stderr, but are otherwise ignored, and thus may escape notice.
  • Executable Python files should be limited to only scripts which are not run via Bazel-generated Python proxy scripts. (The proxy scripts are those run via bazel run, bazel test, or ./bazel-bin/....) If a script qualifies, use the following “shebang” line:
    #!/usr/bin/env python3
    Rationale: /usr/bin/env enables a PATH search for the Python 3 executable. This is also recommended by PEP 394.

Java Style

We also strictly follow the Google Java Style Guide. Here are some additional comments:

  • Every class and method should have a brief _javadoc_ associated with it.
  • All Java classes should be in packages relative to the Drake root, e.g.: package drake.examples.Pendulum

LCM Style

  • LCM types are under_scored with a leading lcmt_ added. If the type is specific to a particular robot, then it begins with lcmt_robotname_.
  • Variable names in LCM types follow the rules above.

Shell Script Style

We follow the Google Shell Style Guide.