Python编程中实现迭代器的一些技巧小结

>>> def test_yield():
... yield 1
... yield 2
... yield (1,2)
...
>>> a = test_yield()
>>> a.next()
1
>>> a.next()
2
>>> a.next()
(1, 2)
>>> a.next()
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
StopIteration

def fab(max): 
 n, a, b = 0, 0, 1 
 while n < max:
 print b, "is generated" 
 yield b
 a, b = b, a + b 
 n = n + 1 

>>> for item in fab(5):
... print item
... 
1 is generated
1
1 is generated
1
2 is generated
2
3 is generated
3
5 is generated
5

>>> temp_gen = fab(5)
>>> dir(temp_gen)
['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'gi_code', 'gi_frame', 'gi_running', 'next', 'send', 'throw']

>>> temp_gen = (x for x in range(5))
>>> temp_gen
<generator object <genexpr> at 0x7192d8>
>>> for item in temp_gen:
... print item
... 
0
1
2
3
4
>>> dir(temp_gen)
['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'gi_code', 'gi_frame', 'gi_running', 'next', 'send', 'throw']

>>> iter('abc')
<iterator object at 0x718590>
>>> str_iterator = iter('abc')
>>> next(str_iterator)
'a'
>>> next(str_iterator)
'b'
>>> lst_gen = iter([1,2,3,4])
>>> lst_gen
<listiterator object at 0x728e30>
>>> dir(lst_gen)
['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__length_hint__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'next']

>>> help(iter)
Help on built-in function iter in module builtins:

iter(...)
 iter(iterable) -> iterator
 iter(callable, sentinel) -> iterator

 Get an iterator from an object. In the first form, the argument must
 supply its own iterator, or be a sequence.
 In the second form, the callable is called until it returns the sentinel.