[Python-ideas] Disallow importing the same module under multiple names

[Brendan Barnwell]

On 2018-03-14 04:18, Steven D'Aprano wrote:
> Apart from intentionally manipulating sys.modules or the import system,
> or playing file system tricks like hard-linking your files, under what
> circumstances can this occur by accident?

	It can occur if a given directory winds up appearing twice on the 
import path.  For instance, if /foo is on the path and /foo/bar is a 
package directory with /foo/bar/baz as a subpackage directory, then you 
can do "from bar import baz" and "import baz" and wind up with two 
different module objects referring to the same module.

	This usually happens when code starts adding paths to sys.path.  This 
is in some sense "manipulating the import system" but it's something 
that a fair number of libraries do in various contexts, in order to be 
able to do things like import plugins without requiring the user to make 
those plugins available on the default import path.

	For what it's worth, I have been bitten by the problem a few times, 
although it's not very common.  I think it's worth considering the 
proposal, but not sure if any change is justified given that the issue 
is fairly obscure.

-- 
Brendan Barnwell
"Do not follow where the path may lead.  Go, instead, where there is no 
path, and leave a trail."
    --author unknown