[Python-ideas] Implicit submodule imports

[Andrew Barnert]

On Sep 26, 2014, at 17:33, Steven D'Aprano <steve at pearwood.info> wrote:

> On Fri, Sep 26, 2014 at 12:43:12PM -0700, Ethan Furman wrote:
> 
>> What about
>> 
>>  Option 4: have reload work with modules converted into classes
>> 
>> ?
>> 
>> This may mean having some extra fields in the class, and probably some 
>> extra code in the module loading, but it might be the simplest approach.
> 
> 
> I don't know that this is strictly necessary. You can put anything you 
> like into sys.modules, and reload() just raises a TypeError:
> 
> 
> py> sys.modules['spam'] = 23
> py> import spam
> py> spam
> 23
> py> reload(spam)
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> TypeError: reload() argument must be module
> 
> 
> Since reload() is mostly intended as a convenience at the REPL, I'd be 
> willing to forgo that convenience for special "modules".
> 
> Or perhaps these special "modules" could subclass ModuleType and somehow 
> get reloading to work correctly. In 2.7 at least you can manually copy a 
> module to a module subclass, install it into sys.modules, and reload 
> will accept it. Not only that, but after reloading it still uses the 
> same subclass.
> 
> Unfortunately, when I tried it in 3.3, imp.reload complained about my 
> custom module subclass not being a module, so it seems that 3.3 at least 
> is more restrictive than 2.7. (Perhaps 3.3 reload does a "type(obj) is 
> ModuleType" instead of isinstance test?)

I don't know about 3.3 (and who cares?), but in trunk it's an isinstance test:

https://hg.python.org/cpython/file/default/Lib/importlib/__init__.py#l115


> Nevertheless, I got this proof of concept more-or-less working in 2.7 
> and 3.3:
> 
> import sys
> from types import ModuleType
> 
> class MagicModule(ModuleType):
>    def __getattr__(self, name):
>        if name == "spam":
>            return "Spam spam spam!"
>        raise AttributeError
> 
> eggs = 23
> 
> _tmp = MagicModule(__name__)
> _tmp.__dict__.update(sys.modules[__name__].__dict__)
> sys.modules[__name__] = _tmp
> del _tmp
> 
> 
> 
> -- 
> Steven
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