Oh, I'm shame myself. Only when `from email import *` is used, __all__ submodules are imported. INADA Naoki <songofacandy@gmail.com> On Mon, Sep 11, 2017 at 12:17 PM, Guido van Rossum <guido@python.org> wrote:
I don't think submodules are automatically imported, unless there are import statements in __init__.py.
On Sun, Sep 10, 2017 at 8:08 PM, INADA Naoki <songofacandy@gmail.com> wrote:
It looks simple and easy to understand.
To achieve lazy import without breaking backward compatibility, I want to add one more rule: When package defines both of __getattr__ and __all__, automatic import of submodules are disabled (sorry, I don't have pointer to specification about this behavior).
For example, some modules depends on email.parser or email.feedparser. But since email/__init__.py uses __all__, all submodules are imported eagerly.
See https://github.com/python/cpython/blob/master/Lib/email/__init__.py#L7-L25
Changing __all__ will break backward compatibility. With __getattr__, this can be lazy import:
import importlib
def __getattr__(name): if name in __all__: return importlib.import_module("." + name, __name__) raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
Regards,
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