Python

All Python code should conform to the guidelines in PEP8. In particular:

• Indent each level using 4 spaces (U+0020 SPACE), and no TABs (U+0008 CHARACTER TABULATION).

• Name modules in lower case, multiplewordslikethis.

• Name classes in title case, MultipleWordsLikeThis.

• Name functions, instances and other variables in lower case, multiple_words_like_this.

• Every module, class, and function has a Python doc string.

• Doc strings are written as triple-quoted strings.

  • The first line is a one-line summary of the object. This summary line appears on the same line as the opening triple-quote, separated by a single space.
  • Further lines, if needed, are separated from the first by one blank line.
  • The closing triple-quote appears on a separate line.

  Example:

  def frobnicate(spam):
      """ Perform frobnication on ``spam``.
  
          The frobnication is done by the Dietzel-Venkman algorithm,
          and optimises for the case where ``spam`` is freebled and
          agglutinative.
  
          """
      spagnify(spam)
      # …
  

• All import statements appear at the top of the module.

• Each import statement imports a single module, or multiple names from a single module.

  Example:

  import sys
  import os
  from spam import foo, bar, baz
  

Additional style guidelines:

• A page break (U+000C FORM FEED) whitespace character is used within a module to break up semantically separate areas of the module.

Test-driven development

Where possible, practice test-driven development to implement program code.

• During a development session, maintain a separate window or terminal with the unit test suite for the project running continuously, or automatically every few seconds.
• Any time a test is failing, the only valid change is to make all tests pass.
• Develop new interface features (changes to the program unit's behaviour) only when all current tests pass.
• Refactor as needed, but only when all tests pass.
  • Refactoring is any change to the code which does not alter its interface or expected behaviour, such as performance optimisations, readability improvements, modularisation improvements etc.
• Develop new or changed program behaviour by:
  • First write a single, specific test case for that new behaviour, then watch the test fail in the absence of the desired behaviour.
  • Implement the minimum necessary change to satisfy the failing test. Continue until all tests pass again, then stop making functional changes.
  • Once all tests (including the new test) pass, consider refactoring the code and the tests immediately, then ensure all the tests pass again after any changes.
  • Iterate for each incremental change in interface or behaviour.

Test-driven development is not absolutely necessary, but is the simplest, most direct way to generate the kind of program changes accompanied by unit tests that are necessary for inclusion in the project.