My package has the following structure:
mobilescouter/
__init__.py #1
mapper/
__init__.py #2
lxml/
__init__.py #3
vehiclemapper.py
vehiclefeaturemapper.py
vehiclefeaturesetmapper.py
...
basemapper.py
vehicle/
__init__.py #4
vehicle.py
vehiclefeature.py
vehiclefeaturemapper.py
...
I'm not sure how the __init__.py
files should be correctly written.
The __init__.py #1
looks like:
__all__ = ['mapper', 'vehicle']
import mapper
import vehicle
But how should for example __init__.py #2
look like? Mine is:
__all__ = ['basemapper', 'lxml']
from basemaper import *
import lxml
When should be __all__
used?
The __init__.py file makes Python treat directories containing it as modules. Furthermore, this is the first file to be loaded in a module, so you can use it to execute code that you want to run each time a module is loaded, or specify the submodules to be exported.
The __init__.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path.
If you have setup.py in your project and you use find_packages() within it, it is necessary to have an __init__.py file in every directory for packages to be automatically found.
__all__
is very good - it helps guide import statements without automatically importing modules
http://docs.python.org/tutorial/modules.html#importing-from-a-package
using __all__
and import *
is redundant, only __all__
is needed
I think one of the most powerful reasons to use import *
in an __init__.py
to import packages is to be able to refactor a script that has grown into multiple scripts without breaking an existing application. But if you're designing a package from the start. I think it's best to leave __init__.py
files empty.
for example:
foo.py - contains classes related to foo such as fooFactory, tallFoo, shortFoo
then the app grows and now it's a whole folder
foo/
__init__.py
foofactories.py
tallFoos.py
shortfoos.py
mediumfoos.py
santaslittlehelperfoo.py
superawsomefoo.py
anotherfoo.py
then the init script can say
__all__ = ['foofactories', 'tallFoos', 'shortfoos', 'medumfoos',
'santaslittlehelperfoo', 'superawsomefoo', 'anotherfoo']
# deprecated to keep older scripts who import this from breaking
from foo.foofactories import fooFactory
from foo.tallfoos import tallFoo
from foo.shortfoos import shortFoo
so that a script written to do the following does not break during the change:
from foo import fooFactory, tallFoo, shortFoo
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