[tahoe-dev] startup error after upgrade

Daira Hopwood (formerly David-Sarah) david-sarah at jacaranda.org
Tue Apr 2 07:41:42 UTC 2013


On 29/03/13 22:06, Zooko Wilcox-O'Hearn wrote:
> I thought the design flaw in question was:
> 
> When you "import foo", and there are multiple modules named "foo" in your filesystem, then
> which specific module you get is determined by a list of directories, each of which can
> contain multiple modules. Therefore, when you add a directory to the front of that list
> you are prioritizing *all* of the modules in that directory over any other modules by the
> same name in any other directories. Therefore, if a single directory contains both a
> module you want to import and a module that you mustn't import (because it name-collides
> with another module that you want to import), then you have to make sure the *other*
> directory is earlier than this one on the list.

Yes.

> If there is a cycle of such dependencies, then it is impossible to import all the modules
> that you require.

But the original assumption was that you would never have multiple versions of a single
package installed. That is, if you wanted to install a new version, you'd uninstall any
older version (and put up with any backward compatibility issues). In that case, there
would be no "module that you mustn't import" in the same place as a "module you want to
import".

setuptools promises to allow you to install multiple versions, and that's what fails to
work.

-- 
Daira Hopwood ⚥  (formerly David-Sarah)

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