< turn >python: __init__.py usage

Transfer from http://www.cnblogs.com/BeginMan/p/3183629.html

Python has a __init__.py file in each of the module's packages, and with this file we can import the module in this directory.
So, what other functions does __init__.py have?
In fact, __init__.py inside can still have content, we import a package, actually imported its __init__.py file.
We can then import other packages, or modules, into the __init__.py file.
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This way, when we import this package, the __init__.py file runs automatically. To help us import so many modules, we do not need to write all the import statements in a file, but also reduce the amount of code.
There is no need to import the module.
There is also an important variable in __init__.py, called __all__. We sometimes take a trick of "import All", which is this:
From PackageName Import *
Import then imports the sub-modules and sub-packages that are registered in the __ALL__ list in the package __init__.py file into the current scope. Like what:
#文件 __init__.py

__all__ = ["Module1", "Module2", "SubPackage1", "SubPackage2"]

such as: In a bag with foo.py, __init__.py

#__init__.pyimport osimport datetime   

#foo.pyimport *print Datetime.datetime.now ()  

Then output: 2013-07-11 11:34:41.250000

< turn >python: __init__.py usage