Finder_Bas (original) (raw)

Guido van Rossum guido at python.org
Fri Apr 21 18:39:37 CEST 2006

On 4/21/06, Thomas Wouters <thomas at python.org> wrote:

On 4/21/06, guido.van.rossum <python-3000-checkins at python.org> wrote: > The hardest part was fixing two mutual recursive imports; > somehow changing "import foo" into "from . import foo" where > foo and bar import each other AND both are imported from init.py caused things to break. Bah. Hm, this is possibly a flaw in the explicit relative import mechanism. Normal circular imports work because a module object is stuffed into sys.modules before any code for the module is executed, so the next 'import' of that module just finds the half-loaded module object. I guess 'from . import name' really looks at the package contents, though, and there, the module isn't stored until it's done loading. I'm not sure why it raises a 'cannot import name' exception instead of recursing into a spiral of death, but I guess that's a good thing. :)

That's what I thought. But I believe I reproduced it in 2.4 as well. I'm not 100% sure but I've got a feeling that the situation is actually due to these imports happening while init is loading. When P is a package and M is a module, "from P import M" seems to first check that sys.modules["P.M"] exists, but then it somehow asks for P.M instead for sys.modules["P.M"]. At least that's how I cam up with the fix (which sets P.M from inside M) and the fix made the problem go away.

Should this be fixed, or is it an esoteric enough case that I shouldn't bother?

I do think it ought to be fixed, and in 2.5 as well.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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