Python Cookbook, 3rd Edition

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1. 4.1. Manually Consuming an Iterator
   
2. Problem
   
3. You need to process items in an iterable, but for whatever reason, you can’t or don’t want
   
4. to use a for loop.
   
5. Solution
   
6. To manually consume an iterable, use the next() function and write your code to catch
   
7. the StopIteration exception. For example, this example manually reads lines from a
   
8. file:
   
9. with open('/etc/passwd') as f:
   
10. try:
    
11. while True:
    
12. line = next(f)
    
13. print(line, end='')
    
14. except StopIteration:
    
15. pass

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1. 4.2. Delegating Iteration
   
2. Problem
   
3. You have built a custom container object that internally holds a list, tuple, or some other
   
4. iterable. You would like to make iteration work with your new container.
   
5. Solution
   
6. Typically, all you need to do is define an __iter__() method that delegates iteration to
   
7. the internally held container. For example:
   
8. class Node:
   
9. def __init__(self, value):
   
10. self._value = value
    
11. self._children = []
    
12. def __repr__(self):
    
13. return 'Node({!r})'.format(self._value)
    
14. def add_child(self, node):
    
15. self._children.append(node)
    
16. def __iter__(self):
    
17. return iter(self._children)
    
18. # Example
    
19. if __name__ == '__main__':
    
20. root = Node(0)
    
21. child1 = Node(1)
    
22. child2 = Node(2)
    
23. root.add_child(child1)
    
24. root.add_child(child2)
    
25. for ch in root:
    
26. print(ch)
    
27. # Outputs Node(1), Node(2)

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多谢 多谢

tzj110 发表于 2014-7-22 13:43

非常感谢。楼主辛苦！！

楼主威武，多谢分享~

听说中文版错误多，直接来看英文版了