環(huán)境:python 2.7.11,python3.5基本相同。

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Python Module

模塊可以包括函數(shù)定義以及一些語(yǔ)句（用于初始化模塊，因此只在第一次import語(yǔ)句被執(zhí)行時(shí)調(diào)用）。
模塊擁有私有的符號(hào)表（作為模塊內(nèi)所有函數(shù)的全局符號(hào)表），所以在編寫(xiě)模塊時(shí)可以不用擔(dān)心與用戶(hù)的全局變量發(fā)生命名沖突的情況。

Import Module

# ./fibo.py
# ./main.py

# main.py
from fibo import fib

or

import fibo 
fib = fibo.fib

值得一提的是，在module中也可以定義__all__（見(jiàn)下文）
另外除非在__all__加入，import會(huì)自動(dòng)忽略以_開(kāi)頭的函數(shù)。

Packages

包是一種組織模塊命名空間的方式。

For example, the module name A.B designates a submodule named B in a package named A.

example

sound/                          Top-level package
     __init__.py               Initialize the sound package
     formats/                  Subpackage for file format conversions
           __init__.py
           wavread.py
           wavwrite.py
           aiffread.py
           aiffwrite.py
           auread.py
           auwrite.py
           ...
   effects/                  Subpackage for sound effects
           __init__.py
           echo.py
           surround.py
           reverse.py
           ...
   filters/                  Subpackage for filters
           __init__.py
           equalizer.py
           vocoder.py
           karaoke.py
           ...

__init__.py

含有__init__.py文件的文件夾才會(huì)被Python認(rèn)為是一個(gè)包。__init__.py 可以為空，也可以有用于初始化包的語(yǔ)句。

When import individual modules from the package, it must be referenced with its full name.

Import:

import sound.effects.echo

When Use:

sound.effects.echo.echofilter(input, output, delay=0.7, atten=4)

import * from a package

When

from sound.effects import *

理想情況下，這個(gè)語(yǔ)句會(huì)遍歷整個(gè)文件夾，然后import全部模塊。但是，這不是python的實(shí)現(xiàn)方式。
因此需要在__init__.py中顯式地定義名為__all__的list。此時(shí)上述語(yǔ)句會(huì)import``__all__中的所有模塊。

all = ["echo", "surround", "reverse"]

If __all__ is not defined, the statement from sound.effects import * does not import all submodules from the package sound.effects into the current namespace; it only ensures that the package sound.effects has been imported (possibly running any initialization code in __init__.py) and then imports whatever names are defined in the package.

**This **includes:

• any names defined (and submodules explicitly loaded) by __init__.py.
• any submodules of the package that were explicitly loaded by previous import statements.

For example:

import sound.effects.echo
import sound.effects.surround
from sound.effects import *

In this example, the echo and surround modules are imported in the current namespace because they are defined in the sound.effects package when the from...import statement is executed.

Intra-package References

When packages are structured into subpackages (as with the sound package in the example), you can use absolute imports as well as relative imports

Explicit relative import

from . import echo
from .. import formats
from ..filters import equalizer

Reference

To learn more, look up the DOCs @here