Core Python Programming (2nd Edition)

Furthermore, we can go down one more subpackage for referencing:
from Phone.Mobile import Analog
Analog.dial('555-1212')
In fact, you can go all the way down in the subpackage tree structure:
from Phone.Mobile.Analog import dial
dial('555-1212')
In our above directory structure hierarchy, we observe a number of __init__.py files. These are
initializer modules that are required when using from-import to import subpackages but they can be
empty if not used. Quite often, developers forget to add _inti_.py files to their package directories, so
starting in Python 2.5, this triggers an ImportWarning message.
However, it is silently ignored unless the -Wd option is given when launching the interpreter.
12.7.2. Using from-import with Packages
Packages also support the from-import all statement:
from package.module import *
However, such a statement is dependent on the operating system's filesystem for Python to determine
which files to import. Thus the __all__ variable in __init__.py is required. This variable contains all the
module names that should be imported when the above statement is invoked if there is such a thing. It
consists of a list of module names as strings.
12.7.3. Absolute Import
As the use of packages becomes more pervasive, there have been more cases of the import of
subpackages that end up clashing with (and hiding or shadowing) "real" or standard library modules
(actually their names). Package modules will hide any equivalently-named standard library module
because it will look inside the package first to perform a relative import, thus hiding access to the
standard library module.
Because of this, all imports are now classified as absolute, meaning that names must be packages or
modules accessible via the Python path (sys.path or PYTHONPATH).