Python里的enumerate

谁借莪１个温暖的怀抱￠ 2022-08-27 13:48 199阅读 0赞

刚刚看了一下Python里面的enumerate的部分， enumerate每次回返回一个tuple：(index, value)

例子很简单：

for i, v in enumerate(['tic', 'tac', 'toe']):
        print i,v

在enumerate里面我们可以放置一个iterable的对象，这样的对象可以是a sequence, an iterator, or some other object which supports iteration。在Python doc 里面看到这样的解释之后我便尝试自己实现一个iterable的对象。实现如下：

class Enumerable:
        def __init__(self):
            self.value = 1
        def __iter__(self):
            return self
        def next(self):
            if (self.value > 10):
                raise StopIteration
            else:
                self.value += 1
                return self.value
    
    enum = Enumerable()
    for i, v in enumerate(enum):
        print i, v

只需要实现\_\_iter\_\_和next接口就可以了

enumerate(iterable)  
Return an enumerate object. iterable must be a sequence, an iterator, or some other object which supports iteration. The next() method of the iterator returned by enumerate() returns a tuple containing a count (from zero) and the corresponding value obtained from iterating over iterable. enumerate() is useful for obtaining an indexed series: (0, seq\[0\]), (1, seq\[1\]), (2, seq\[2\]), .... New in version 2.3.  
  
  
A new built-in function, enumerate(), will make certain loops a bit clearer. enumerate(thing), where thing is either an iterator or a sequence, returns a iterator that will return (0, thing\[0\]), (1, thing\[1\]), (2, thing\[2\]), and so forth.  
  
  
A common idiom to change every element of a list looks like this:

for i in range(len(L)):
        item = L[i]
        # ... compute some result based on item ...
        L[i] = result

This can be rewritten using enumerate() as:

for i, item in enumerate(L):
        # ... compute some result based on item ...
        L[i] = result

转自：http://taoyh163.blog.163.com/blog/static/195803562008196235218/