Lazy sub-module import

[noklam]

Description

Is your feature request related to a problem? A clear and concise description of what the problem is: "I'm always frustrated when ..."
Inspired by @deepyaman #2673, https://peps.python.org/pep-0562/ shows some new way of doing lazy imports. It may change the discussion in #712.

# lib/__init__.py

import importlib

__all__ = ['submod', ...]

def __getattr__(name):
    if name in __all__:
        return importlib.import_module("." + name, __name__)
    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

# lib/submod.py

print("Submodule loaded")
class HeavyClass:
    ...

# main.py

import lib
lib.submod.HeavyClass  # prints "Submodule loaded"

Context

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Possible Implementation

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[noklam]

It's not ready for grooming yet, but I have a feeling this can be useful so I have to write it down first as I have very bad memory.