[Python-Dev] Re: Allow all assignment expressions after 'import something as' (original) (raw)

Guido van Rossum guido@beopen.com
Wed, 23 Aug 2000 11:22:04 -0500

On Mon, 21 Aug 2000, Guido van Rossum wrote: > > > > > Summary: Allow all assignment expressions after 'import > > > > > something as' [...] > I kind of doubt it, because it doesn't look useful.

[Ping]

Looks potentially useful to me. If nothing else, it's certainly easier to explain than any other behaviour i could think of, since assignment is already well-understood.

KISS suggests not to add it. We had a brief discussion about this at our 2.0 planning meeting and nobody there thought it would be worth it, and several of us felt it would be asking for trouble.

> I do want "import foo.bar as spam" back, assigning foo.bar to spam.

No no no no. Or at least let's step back and look at the whole situation first. "import foo.bar as spam" makes me uncomfortable because: (a) It's not clear whether spam should get foo or foo.bar, as evidenced by the discussion between Gordon and Thomas.

As far as I recall that conversation, it's just that Thomas (more or less accidentally) implemented what was easiest from the implementation's point of view without thinking about what it should mean. Of course it should mean what I said if it's allowed. Even Thomas agrees to that now.

(b) There's a straightforward and unambiguous way to express this already: "from foo import bar as spam".

Without syntax coloring that looks word soup to me.

import foo.bar as spam

uses fewer words to say the same clearer.

(c) It's not clear whether this should work only for modules named bar, or any symbol named bar.

Same as for import: bar must be a submodule (or subpackage) in package foo.

Before packages, the only two forms of the import statement were:

import from import After packages, the permitted forms are now: import import import . import . from import from import from . import from . import

You're creating more cases than necessary to get a grip on this. This is enough, if you realize that a package is also a module and the package path doesn't add any new cases:

import from import from import

where a is a dot-separated list of package names.

With "as" clauses, we could permit: import as import as ?? import . as ?? import . as ?? import . as ?? import .. as from import as from import as from . import as from . import as

Let's simplify that to:

import as from import as from import as

It's not clear that we should allow "as" on the forms marked with ??, since the other six clearly identify the thing being renamed and they do not.

Also note that all the other forms using "as" assign exactly one thing: the name after the "as". Would the forms marked with ?? assign just the name after the "as" (consistent with the other "as" forms), or also the top-level package name as well (consistent with the current behaviour of "import .")? That is, would import foo.bar as spam define just spam or both foo and spam?

Aargh! Just spam, of course!

All these questions make me uncertain...

Not me.

--Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)