Python Coding style

Coding style

Black is the tool used to reformat the Python code.


The Python linting is done by Flake8 and pylint They are executed by mozlint both at review phase and in the CI.


Four spaces in Python code.

Makefile/ practices

  • Changes to makefile and variables do not require build-config peer review. Any other build system changes, such as adding new scripts or rules, require review from the build-config team.

  • Suffix long if/endif conditionals with #{ & #}, so editors can display matched tokens enclosing a block of statements.

    ifdef CHECK_TYPE #{
      ifneq ($(flavor var_type),recursive) #{
        $(warning var should be expandable but detected var_type=$(flavor var_type))
      endif #}
    endif #}
  • are python and follow normal Python style.

  • List assignments should be written with one element per line. Align closing square brace with start of variable assignment. If ordering is not important, variables should be in alphabetical order.

    var += [
  • Use CONFIG['TARGET_CPU'] {=arm} to test for generic classes of architecture rather than CONFIG['OS_TEST'] {=armv7} (re: bug 886689).

Other advices

  • Install the mozext Mercurial extension, and address every issue reported on commit or the output of hg critic.

  • Follow PEP 8. Please run Black for this.

  • Do not place statements on the same line as if/elif/else conditionals to form a one-liner.

  • Global vars, please avoid them at all cost.

  • Exclude outer parenthesis from conditionals.Use if x > 5:,rather than if (x > 5):

  • Use string formatters, rather than var + str(val). var = 'Type %s value is %d'% ('int', 5).

  • Testing/Unit tests, please write them and make sure that they are executed in the CI.