[Import-SIG] Round 2 for "A ModuleSpec Type for the Import System"

[Brett Cannon]

On Wed, Aug 28, 2013 at 12:04 PM, Eric Snow <ericsnowcurrently at gmail.com>wrote:

> On Wed, Aug 28, 2013 at 8:43 AM, Eric Snow <ericsnowcurrently at gmail.com>wrote:
>
>> On Aug 28, 2013 3:26 AM, "Nick Coghlan" <ncoghlan at gmail.com> wrote:
>> > I realised that if we're going to allow mutating the spec in create,
>> we're going to have to promise not to reuse them across load calls. So
>> loaders can be shared, but specs can't.
>>
>> The latest version of the PEP already specifies that each module will
>> have its own copy, even if the spec is otherwise the same.  Perhaps it
>> should also make clear that loading_info should not be shared between
>> specs.  It wouldn't hurt to also say something about allowing only one call
>> to load() or something along those lines
>>
> I see three options:
>
> 1. We advise against calling Modulespec.create() and ModuleSpec.load()
> more than once.
> 2. ModuleSpec's create() and load() programmatically disallow (or
> otherwise handle) being called more than once.
> 3. Dictate that Loader.create_module() must handle the case where it is
> called more than once.  Fail?  Return None?  Return the same module as
> before?
>
> I'll advocate for 3 along with making sure ModuleSpec.create() correctly
> handles the exceptional response of Loader.create_module().  However, the
> PEP does not really specify what happens when create() and load() are
> called multiple times.  That needs to be added.  I'm tempted to have load()
> simply return whatever is in sys.modules and bypass loading if the module
> is already loaded.
>

Isn't that the point of reload() sans the blind return? This is heading
down the road of trying to worry about stuff that will likely never happen
except by people trying to bypass the import system and thus are just
asking to get screwed up. We shouldn't bend over to block or (or support
it).

-Brett


>  And create() would simply return a new, prepared module, with special
> handling for the Loader.create_module() exceptional case.
>
> Really, the sticky part is the (potential) call to Loader.create_module()
> in ModuleSpec.create().  Otherwise it should not matter.  ModuleSpec.exec()
> should be able to be called as many times as desired, just like
> Loader.load_module() (and Loader.exec_module()).
>
> -eric
>
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