linusg linusg - 1 year ago 133
Python Question

Coding style (PEP8) - Module level "dunders"

Definition of "Dunder" (Double underscore):

I have a question according the placement of module level "dunders" (like
etc.) in Python code.

The question came up to me while reading through PEP8 and seeing this SO question.

The accepted answer says:

is a global "variable" and should therefore appear below the imports.

But in the PEP8 section Module level dunder names I read the following:

Module level "dunders" (i.e. names with two leading and two trailing
underscores) such as
, etc. should
be placed after the module docstring but before any import statements
except from
imports. Python mandates that future-imports
must appear in the module before any other code except docstrings.

They also give an code example:

"""This is the example module.

This module does stuff.

from __future__ import barry_as_FLUFL

__all__ = ['a', 'b', 'c']
__version__ = '0.1'
__author__ = 'Cardinal Biggles'

import os
import sys

But when I put the following into PyCharm, I see this warning:

PEP8: module level import not at top of file

Pycharm ignoring PEP8?

Question: What is the correct way to store these variables with double underscores?

Answer Source

PEP 8 recently was updated to put the location before the imports. See revision cf8e888b9555, committed on June 7th, 2016:

Relax __all__ location.

Put all module level dunders together in the same location, and remove the redundant version bookkeeping information.

Closes #27187. Patch by Ian Lee.

The text was further updated the next day to address the from __future__ import ... caveat.

The patch links to issue #27187, which in turn references this pycodestyle issue, where it was discovered PEP 8 was unclear.

Before this change, as there was no clear guideline on module-level dunder globals, so PyCharm and the other answer were correct at the time. I'm not sure how PyCharm implements their PEP 8 checks; if they use the pycodestyle project (the defacto Python style checker), then I'm sure it'll be fixed automatically. Otherwise, perhaps file a bug with them to see this fixed.

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