[Python-Dev] Relative import (original) (raw)

Ken Manheimer klm at zope.com
Tue Dec 23 12:03:00 EST 2003

On Mon, 22 Dec 2003, Devin wrote:

The first part stems from Guido's idea about using a '.' at the beginning of a relative import. It seemed a bit weird at first, but I eventually became very comfortable with the idea after thinking about it in respect to absolute imports. I'll explain what I mean.

If you currently want to import a module 'a.b.c.d', you write: import a.b.c.d Now, if you're in the module 'a.b', you could still write: import a.b.c.d ... but the 'a.b' part is redundant because you're already in the module 'a.b'. If you take away 'a.b', then you end up with: import .c.d

I also look at it this way, and find it both intuitive and mnemonic. My model is slighly different than yours, though, in a way that simplifies the expression for going up the relative chain. I'll explain...

This flowed well in my head, and looks natural. However, the suggestion about '.' or '..' referring to the parent looks ugly and unnatural.

Let's say '.' was used to spell "parent module", and let's assume that the module 'a.b.c.d' wants to import 'a.b.e'. The absolute import would be spelled: import a.b.e ... and the relative import would be spelled: import .....e # .[parent].[parent].e Yuck! (no offense :)

Truly, yuck. But in my model, the leading '.' dot, itself, stands for the containing package, and '..' stands for the containing package's package, and so forth:

import ..e # [parent-of-parent].e

I don't think it's yucky at all, this way. (I also don't think it's un-pythonic - python uses punctuation all over to denote type literals ('{'/'}'), cues which delineate statement suites (':'), and so forth.) In fact, i think it's a lot more mnemonic and encompassing than the alternatives that use words (though i haven't looked at all the alternatives very carefully yet).

Even using the leading '.' syntax, it would be good to have a specific identifier for the containing package, realized in each module and respected as a special identifier by the package machinery. I like 'pkg':

import pkg.sibling # == 'import .sibling'

and

import pkg.pkg.uncle # == 'import ..uncle' import pkg.pkg.uncle.cousin # == 'import ..uncle.cousin'

I think the leading '.' dot forms are a lot nicer, but the presence of a module named 'pkg' would be useful for programmatically mucking navigating the package structure.

Ken Manheimer klm at zope.com

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