迭代器和生成器

Posted 2021-01-22 shaopan

迭代器(iterator) 

迭代器协议：必须拥有__iter__方法和__next__方法。

1）迭代的概念

#迭代器即迭代的工具，那什么是迭代呢？
#迭代是一个重复的过程，每次重复即一次迭代，并且每次迭代的结果都是下一次迭代的初始值
while True: #只是单纯地重复，因而不是迭代
    print(‘===>‘) 
    
L=[1,2,3]
count=0
while count < len(L): #迭代
    print(l[count])
    count+=1

#dir() ----(展示所拥有的方法) 
print(dir([1,2])) 
print(dir((2,3)))
print(dir({‘a‘:1,‘b‘:2}))
print(dir({1,2,3,4}))
##以下所展示的有双下方法：如‘__add__‘, ‘__class__‘它们是Python解释器的内部方法，也称为双下方法。是由C语言写的，可能不止一种方式调用它。

# [‘__add__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__delitem__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__gt__‘, ‘__hash__‘, ‘__iadd__‘, ‘__imul__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__mul__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__reversed__‘, ‘__rmul__‘, ‘__setattr__‘, ‘__setitem__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘append‘, ‘clear‘, ‘copy‘, ‘count‘, ‘extend‘, ‘index‘, ‘insert‘, ‘pop‘, ‘remove‘, ‘reverse‘, ‘sort‘] # [‘__add__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__getnewargs__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__mul__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__rmul__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘count‘, ‘index‘] # [‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__delitem__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__setitem__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘clear‘, ‘copy‘, ‘fromkeys‘, ‘get‘, ‘items‘, ‘keys‘, ‘pop‘, ‘popitem‘, ‘setdefault‘, ‘update‘, ‘values‘] # [‘__and__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__gt__‘, ‘__hash__‘, ‘__iand__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__ior__‘, ‘__isub__‘, ‘__iter__‘, ‘__ixor__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__ne__‘, ‘__new__‘, ‘__or__‘, ‘__rand__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__ror__‘, ‘__rsub__‘, ‘__rxor__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__sub__‘, ‘__subclasshook__‘, ‘__xor__‘, ‘add‘, ‘clear‘, ‘copy‘, ‘difference‘, ‘difference_update‘, ‘discard‘, ‘intersection‘, ‘intersection_update‘, ‘isdisjoint‘, ‘issubset‘, ‘issuperset‘, ‘pop‘, ‘remove‘, ‘symmetric_difference‘, ‘symmetric_difference_update‘, ‘union‘, ‘update‘]

##双下方法:

print([1].__add__([2]))
print([1]+[2])
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[1, 2]
[1, 2]