[Import-SIG] PEP 420: Implicit Namespace Packages

[Barry Warsaw]

On May 03, 2012, at 10:48 AM, Brett Cannon wrote:

>So, to the people not wanting to set __file__, that  (probably) won't fly
>because it has been documented for years that built-in modules are the only
>things that don't define __file__.

Okay, but *why* is this the rule, other than that PEP 302 says it?  IOW, PEP
302 doesn't give much of a rationale for the rule, and I suspect it just
reflected the reality back in 2002.

>Or we at least need to explain to people how to tell the difference in a
>backwards-compatible fashion.

Definitely, and I think that would be fine to include in PEP 420.

>So I would have said that had experience with the stdlib not big me on
>this. In my situation, the trace module was checking file, and if __file__
>didn't contain "<frozen>" or "<doctest" it would try to read it as a path,
>and then error out if it couldn't open the file. Now I updated it to
>startswith('<') and endswith('>'), but I wonder how many people made a
>similar whitelist approach. And while having __file__ to None or
>non-existent will take about the same amount of time to fix, it is less
>prone to silly whitelisting like what the trace module had.

See what I mean about arbitrary and underdocumented? :)

Cheers,
-Barry
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