[Python-Dev] Tweaking PEP 8 guidelines for use of leading underscores

[Steven D'Aprano]

On Mon, Jul 15, 2013 at 10:30:02AM +1000, Nick Coghlan wrote:
> On 15 July 2013 09:48, Steven D'Aprano <steve at pearwood.info> wrote:
> > On 14/07/13 21:09, Nick Coghlan wrote:
> >
> >> Slight adjustment to the proposed wording to ensure completely
> >> undocumented
> >> modules are also considered private:
> >
> >
> > -1 on this adjustment. If somebody cannot be bothered writing a one-line doc
> > string:
> >
> > "This module is private, don't touch."
> >
> > then they certainly shouldn't be allowed to use up a public name for a
> > private module. I don't think we should be encouraging more private,
> > undocumented modules. (Documentation is valuable even for private modules.)
> 
> For context, this arose when I checked PEP 8 after the point was
> raised on distutils-sig that pip uses a public name for its
> implementation module (also pip, same as the CLI), but officially
> exposes no stable public programmatic API.

I don't think we should bless this as official policy, certainly not for 
the standard library. We can't tell external modules what to do, and 
possibly there's nothing we can do about existing undocumented private 
modules, short of renaming them, but I think that at least for new 
additions to the std lib module names should follow the same 
single-underscore convention as functions, classes etc. A single leading 
underscore introduces the private namespace, everything else is public.

I've seen too much undocumented public code to ever assume that lack of 
documentation implies it is private.


> At the moment, according to what little PEP 8 has to say about public
> vs private interfaces, that means a bundled pip would represent a new
> public API, despite the fact that the only documented interface for
> pip is the CLI, not the Python module API.
> 
> Since we've been burned by people assuming private APIs are public in
> the past, I figured it made sense to get the actual standards we
> follow in practice documented properly, *before* anyone further gets
> the wrong idea from "import pip; help(pip)".

I can tell you that people will do that regardless of what PEP 8 has to 
say about "not documented == private". Especially as worded. I'm sure I 
won't be the only person to reason that if a module has a docstring, it 
is therefore documented.

It takes one character to explicitly document a module as private. 
That's much better than expecting people to treat their failure to 
find documentation as an implicit warning.



-- 
Steven