如果class是classinfo元组中某个元素的�类，也会返回True
In [1]: issubclass(int,(int,float))
Out[1]: True
37 创建迭代器类型
使� iter(obj, sentinel), 返回�个可迭代对象, sentinel可省略(�旦迭代到此元素，�即终�)
In [1]: lst = [1,3,5]
In [2]: for i in iter(lst):
...:
...:
print(i)
1
3
5
In [1]: class TestIter(object):
...:
...:
...:
...:
...:
...:
...:
...:
...:
...:
def __init__(self):
self.l=[1,3,2,3,4,5]
self.i=iter(self.l)
def __call__(self): #定义了__call__�法的类的实例是可调�的
item = next(self.i)
print ("__call__ is called,fowhich would return",item)
return item
def __iter__(self): #�持迭代协议(即定义有__iter__()函数)
print ("__iter__ is called!!")
return iter(self.l)
In [2]: t = TestIter()
In [3]: t() # 因为实现了__call__，所以t实例能被调�
__call__ is called,which would return 1
Out[3]: 1
In [4]: for e in TestIter(): # 因为实现了__iter__�法，所以t能被迭代
...:
...:
print(e)
__iter__ is called!!
1
3
2
3
4
5
38 所有对象之根
object 是所有类的基类
In [1]: o = object()
In [2]: type(o)
Out[2]: object
39 打开�件
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