enumerate其实是一个生成器(generator),这个下面会讲到。使用enumerate之后,for循环变得很简单: for (index, item) in enumerate(items): print index, item # compare: index = 0 for item in items: print index, item index += 1 # compare: for i in range(len(items)): print i, items[i] 使用en...
#1.0 itertools模块的count方法(有限循环)defcount(n):whileTrue:yieldn n+= 1c= count(0)#生成器的绝妙之处:它只会在迭代时才会运行,所以死循环也没有问题,返回一个generator#print(c[:]) # TypeError: 'generator' object is not subscriptableimportitertoolsforxinitertools.islice(c, 10, 13):print(x)...
下面我们自定义对象,分别实现这两个方法(getitem(),iter()) classMyObj:def__init__(self,iterable):self._iterable=list(iterable)def__getitem__(self,item):returnself._iterable[item]obj=MyObj([1,2,3])foriinobj:print(i) 如上所示,这里没有实现__iter__方法,只实现了__getitem__方法,也使得My...
def generator_function(): for i in range(10): yield i for item in generator_function(): print(item) 具体执行结果如下: 其实,这个案例并不是非常实用。生成器最佳应用场景是:你不想同一时间将所有计算出来的大量结果集分配到内存当中,特别是结果集里还包含循环。这里需要注意的是:许多Python 2里的标准库...
生成器(generator)是构造新的可迭代对象的一种简单方式。一般的函数执行之后只会返回单个值,而生成器则是以延迟的方式返回一个值序列,即每返回一个值之后暂停,直到下一个值被请求时再继续。要创建一个生成器,只需将函数中的return替换为yeild即可: 调用该生成器时,没有任何代码会被立即执行: ...
candidate=firstelse:series=iter(first)try:candidate=next(series)except StopIteration:ifdefaultis notMISSING:returndefaultraiseValueError(EMPTY_MSG)from Noneifkey is None:forcurrentinseries:ifcandidate<current:candidate=currentelse:candidate_key=key(candidate)forcurrentinseries:current_key=key(current)ifcandi...
return the next item from the container send resumes the generator and “sends” a value that becomes the result of the current yield-expression throw used to raise an exception inside the generator traceback tb_frame frame object at this level tb_lasti index of last attempted instruction in ...
next(iterator[, default])Return the next item from the iterator. If default is given and the iterator is exhausted, it is returned instead of raising StopIteration. 【例子】 [72]: e = (i for i in range(10)) print(e) # <generator object <genexpr> at 0x0000007A0B8D01B0> print(next...
num = [1, 4, -5, 10, -7, 2, 3, -1] filtered_and_squared = ( x**2 for x in num if x > 0 ) print filtered_and_squared# <generator object <genexpr> at 0x00583E18>for item in filtered_and_squared: print item# 1, 16, 100 4,9 ...
To get ["wtf"] from the generator some_func we need to catch the StopIteration exception, try: next(some_func(3)) except StopIteration as e: some_string = e.value >>> some_string ["wtf"]▶ Nan-reflexivity *1.a = float('inf') b = float('nan') c = float('-iNf') # These...