Guido van Rossum email@example.com wrote:
In a recent discussion in a SF patch, I noticed that PEP 328* only seems to support relative imports within packages, while bare import statements use the entirety of sys.path, not solving the shadowing of standard library module names.
Hm. I'm not convinced that there is a *problem* with shadowing of standard library module names. You shouldn't pick a module name that shadows a standard library module, or if you do you shouldn't want to be able to still use those modules that you're shadowing. Anything else is just asking for trouble.
While I personally don't tend to use names previously existing in the standard library, seemingly a large number of people do, hence the not-so-rare threads on comp.lang.python which ask about such things.
More specifically; after a 'from __future__ import absolute_import' statement, any import in the module performing "import foo" will only check for foo in the standard library, and the use of the leading period, "from . import foo", the will signify relative to the current path. **
And how exactly do you define "the standard library"? Anything that's on sys.path? That would seem the only reasonable interpretation to me. So I take it that you want the "script directory" off that path. (Let's for the sake of argument call it ".".)
Sounds reasonable to me, with one caveat; if one were to consider everything on sys.path to be in the standard library, then every script ever written for Python, which doesn't remove the standard ''/'.' from sys.path, would be part of the standard library.
I would suggest, as a replacement definition (probably with a caveat or two), that any module with a reference in the documentation, that also lies on the default sys.path, which is shipped with Python that is distributed at python.org, is part of the standard library.
The lack of a 'from __future__ import absolute_import' statement in a module will not change the import semantic of that module.
It's hard to imagine how this would work. sys.path is global, so either "." is on it, or it isn't. So things in "." are either considered part of the standard library, or they are not; this can't be made dependent on the module's importation of something from __future__.
Perhaps not, but in the process of importing a module into a namespace, one can check for the existance of the object imported from __future__, and ignore or not the "." entry in sys.path.
This allows current code to continue to work, and for those who want to choose names which shadow the standard library modules, a way of dealing with their choices.
My suggested way of dealing with their choices is summarized in the first paragraph of my reply above.
Perfectly reasonable. I can think of examples where it would not be reasonable, but they are quite cooked *wink*.
Alternatively, PEP 328 could be implemented as-is, and a second future import could be defined which offers this functionality, being permanently optional (or on a different timeline) via the future import.
I don't like permanently optional language features; that causes too much confusion. I'd much rather settle on clear semantics that everyone can understand (even if they may disagree).
But I certainly would prefer that the proposed feature becomes a separate PEP which can be discussed, accepted or rejected, and implemented separately from PEP 328, which is complete and accepted and just awaiting someone to implement it.
Sounds good. I'll see what I can do this weekend about getting a proto-pep started.
Essentially, it would ignore the empty path "" in sys.path when the functionality has been enabled via the proper future import in the current module.
But it's not always "" -- it's the directory where the "main" script was found.
Let me explain the biggest problem I see for your proposal: what would be the canonical name for a module imported using your "new relative semantics"? Remember, the canonical name of a module is its __name__ attribute, and the key that finds it in the sys.modules dict. Because there's only one sys.modules dict (barring restricted execution sandboxes), the canonical name must be unique. So if there's a standard library module string, its canonical name is "string". Now suppose you have your own non-standard-linrary module read from a file string.py. What should its canonical name be? It can't be "string" because that's already reserved for the standard library module name.
The best solution I can think of for this off the top of my head is to somehow allow for the arrangement of a pseudo-package named __main__ and to make all these non-standard-library modules reside (logically) in that module. If you can write a PEP along those lines you may be on to something -- but I expect that the way to turn it on is not to import something from __future__ but perhaps from __main__. I'm not exactly sure how to get "." off sys.path, but maybe you can think about that for your PEP proposal. What do you say?
You make very good points about naming in sys.modules. I will think about this and place some options in the proto-pep.
Thank you, - Josiah