15.11.17 12:53, Ivan Levkivskyi пише:
On 15 November 2017 at 08:43, Serhiy Storchaka <storchaka@gmail.com <mailto:storchaka@gmail.com>> wrote:
It is worth to mention that using name as a module global will
bypass __getattr__. And this is intentional, otherwise calling
__getattr__ for builtins will harm a performance.
Good point!
And please document idiomatic way of using a module global with triggering __getattr__. For example if you want to use a lazy loaded submodule.
sys.modules[__name__].foobar
or
from . import foobar
The difference between them that the latter sets the module attribute, thus __getattr__ will be called only once.
Backwards compatibility and impact on performance
================================================= some tools might not yet expect it.. I will add a note to the PEP about this.
What is affect on pydoc, word completion, inspect, pkgutil, unittest?
This is rather gray area. I am not sure that we need to update them in any way, just the people who use __getattr__ should be aware that
This problem is not new, since it was possible to replace a module with a module subclass with overridden __getattr__ and __dir__ before, but now this problem can occur more often.
I would create more standard helpers (for deprecation, for lazy
importing). This feature is helpful not by itself, but because it
will be used for implementing new features. Using __getattr__
directly will need to write a boilerplate code. Maybe when
implementing these helper you will discover that this PEP needs some
additions.
But in which module these helpers should live?
Good question. lazy_import() could be added in importlib (or importlib.util?). The helper that just adds deprecation on importing a name, could be added in importlib too. But I think that it would be better if the deprecated() helper will also create a wrapper that raises a deprecation warning on the use of deprecated function. It could be added in the warnings or functools modules.
I would add also a more general lazy_initialized(). It is something like cached module property. Executes the specified code on first use, and cache the result as a module attribute.
In all these cases the final __getattr__ method should be automatically constructed from different chunks. At the end it could call a user supplied __getattr__. Or maybe the module method __getattr__ should look first at special registry before calling the instance attribute __getattr__()?
def ModuleType.__getattr__(self, name):
if name in self.__properties__:
call self.__properties__[name]()
elif '__getattr__' in self.__dict__:
call self.__dict__['__getattr__'](name)
else:
raise AttributeError
I'm wondering if the __set_name__ mechanism can be extended to modules. What if call the __set_name__() method for all items in a module dict after finishing importing the module?
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