What is __path__ useful for?

Question

I had never noticed the __path__ attribute that gets defined on some of my packages before today. According to the documentation:

Packag

Answer 1

In addition to selecting different versions of a module based on runtime conditions as Syntactic says, this functionality also would allow you to break up your package into multiple pieces / downloads / installs while maintaining the appearance of a single logical package.

Consider the following.

• I have two packages, mypkg and _mypkg_foo.
• _mypkg_foo contains optional module to mypkg, foo.py.
• as downloaded and installed, mypkg doesn't contain a foo.py.

mypkg's __init__.py can do something like so:

try:
    import _mypkg_foo
    __path__.append(os.path.abspath(os.path.dirname(_mypkg_foo.__file__)))
    import mypkg.foo
except ImportError:
    pass

If someone has installed the package _mypkg_foo, then mypkg.foo is available to them. If they haven't, it doesn't exist.