import和可调用对象的实现原理

import 模块名

模块名没有使用字符串的原因是，被赋值给一个同名的变量，利用变量导入模块

 用途：

在自己写的代码中调用自己的包，可以用 __import__ 导入

In [1]: import time

In [2]: print(time.ctime())
Thu Nov  9 17:32:54 2017

In [3]: ti = __import__('time')

In [4]: print(ti.ctime())
Thu Nov  9 17:33:34 2017

一个对象是否可以调用的判断方法， callable(对象名) ，可以调用返回true, 否则返回 false

In [18]: fun()
aah

In [19]: callable(fun)
Out[19]: True

In [20]: dir(fun)
Out[20]:
['__annotations__',
 '__call__',
 '__class__',
 '__closure__',
 '__code__',
 '__defaults__',
 '__delattr__',
 '__dict__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__get__',
 '__getattribute__',
 '__globals__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__kwdefaults__',
 '__le__',
 '__lt__',
 '__module__',
 '__name__',
 '__ne__',
 '__new__',
 '__qualname__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__']

被本身默认为不可调用对象，将类变成可调用对象的方法是在类中重写  __call__ 方法：

In [21]: class obj1():
    ...:     pass
    ...:

In [22]: o1 = obj1()

In [23]: o1()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-23-188e6fb838ce> in <module>()
----> 1 o1()

TypeError: 'obj1' object is not callable

In [28]: callable(o1)
Out[28]: False

In [21]: class obj1():
    ...:     pass
    ...:

In [22]: o1 = obj1()

In [23]: o1()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-23-188e6fb838ce> in <module>()
----> 1 o1()

TypeError: 'obj1' object is not callable

In [24]: class obj2():
    ...:     def __call__(self):
    ...:         print('rewirte')
    ...:

In [25]: o2=obj2()

In [26]: o2()
rewirte

In [27]: callable(o2)
Out[27]: True