On 16 July 2013 22:02, Thomas Wouters <tho...@python.org> wrote: > On Tue, Jul 16, 2013 at 1:40 PM, Nick Coghlan <ncogh...@gmail.com> wrote: >> >> PEP 8 advises developers to use absolute imports rather than explicit >> relative imports. >> >> Why? Using absolute imports couple the internal implementation of a >> package to its public name - you can't just change the top level >> directory name any more, you have to go through and change all the >> absolute imports as well. You also can't easily vendor a package that >> uses absolute imports inside another project either, since all the >> absolute imports will break. > > > The problem with relative imports (both explicit and implicit) is that it > makes it less obvious when you are importing a module under the wrong name. > If a package ends up in sys.path directly (for example, by executing > something that lives inside it directly) then an explicit relative import > directly in the package will fail, but an explicit relative import in a > sub-package won't, and you can end up with the subtly confusing mess of > multiple imports of the same .py file under different names. > >> >> What's the *concrete* benefit of using absolute imports that overcomes >> these significant shortcomings in maintainability and composability? > > In my experience changing the name of a package is problematic for more > reasons than just 'import'. We used to do the put-in-a-package thing for > third-party packages at Google, and we quit doing it because it was just too > painful: it's hard to find all the places that reference the package by name > (think of __import__, or mucking in sys.modules), and it's extra problematic > with packages that contain extension modules. You can't rename a package, > even for 'vendoring a package', without carefully checking whether it'll > work -- unless you don't care if it'll work, of course :) The alternative is > to include a package *without* changing its name (by adding the right > directory, without __init__.py, to sys.path) and that has worked out a lot > better for us.
These are good reasons, but they're not the reasons the PEP currently gives. "Better failure modes" is a good practical benefit :) > Even so, there's no reason for *the standard library* to use explicit > relative imports, and that's what PEP 8 is supposed to cover, right? :) I realised in re-reading the whole thing that we actually admitted defeat on that front back during the last function annotations discussion :) Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
