1. __all__
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from module import *, 默认导出不以下划线开头的所有成员, 但是加了__all__， 导出列表中的所有。
In [1]: from hello import *
In [2]: _name
Out[2]: 'xiaoming'
In [3]: test_hello()
hello
In [4]: age
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-4-cfd449bec15d> in <module>()
----> 1 age
NameError: name 'age' is not defined
In [5]: _test_name()
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-5-3b45bfdd4d41> in <module>()
----> 1 _test_name()
NameError: name '_test_name' is not defined
注意
__all__ 只影响到了 from module import * 这种导入方式，对于 from module import member 或者 import module 导入方式并没有影响，仍然可以从外部导入.
In [6]: from hello import age
In [7]: age
Out[7]: 18
In [8]: import hello
In [9]: hello.age
Out[9]: 18
