返回组项目的Python生成器

Question

我试图做一个生成器，它可以返回列表中只有一个索引“移动”的多个连续项目。类似于DSP中的移动平均滤波器。举例来说，如果我有列表：

l = [1,2,3,4,5,6,7,8,9] 

我希望这样的输出：

[(1,2,3),(2,3,4),(3,4,5),(4,5,6),(5,6,7),(6,7,8),(7,8,9)] 

我做的代码，但它不带过滤器和发电机等，恐怕也将打破由于工作记忆，如果我需要提供一个大的单词列表。

功能gen：

def gen(enumobj, n): 
    for idx,val in enumerate(enumobj): 
     try: 
      yield tuple(enumobj[i] for i in range(idx, idx + n)) 
     except: 
      break 

和示例代码：

words = ['aaa','bb','c','dddddd','eeee','ff','g','h','iiiii','jjj','kk','lll','m','m','ooo'] 
w = filter(lambda x: len(x) > 1, words) 

# It's working with list 
print('\nList:') 
g = gen(words, 4) 
for i in g: print(i) 

# It's not working with filetrs/generators etc. 
print('\nFilter:') 
g = gen(w, 4) 
for i in g: print(i) 

名单不会产生任何东西。代码应该中断，因为无法索引过滤器对象。当然，其中一个答案是强制列表：list(w)。但是，我正在寻找更好的函数代码。我怎样才能改变它，使函数可以接受过滤器等等。我担心内存中列表中的大量数据。

谢谢

Answer 1

使用迭代器，您需要跟踪已读取的值。一个n大小的清单是诀窍。将下一个值附加到列表中，并在每个收益率后放弃顶部项目。

import itertools 

def gen(enumobj, n): 
    # we need an iterator for the `next` call below. this creates 
    # an iterator from an iterable such as a list, but leaves 
    # iterators alone. 
    enumobj = iter(enumobj) 
    # cache the first n objects (fewer if iterator is exhausted) 
    cache = list(itertools.islice(enumobj, n)) 
    # while we still have something in the cache... 
    while cache: 
     yield cache 
     # drop stale item 
     cache.pop(0) 
     # try to get one new item, stopping when iterator is done 
     try: 
      cache.append(next(enumobj)) 
     except StopIteration: 
      # pass to emit progressively smaller units 
      #pass 
      # break to stop when fewer than `n` items remain 
      break 

words = ['aaa','bb','c','dddddd','eeee','ff','g','h','iiiii','jjj','kk','lll','m','m','ooo'] 
w = filter(lambda x: len(x) > 1, words) 

# It's working with list 
print('\nList:') 
g = gen(words, 4) 
for i in g: print(i) 

# now it works with iterators 
print('\nFilter:') 
g = gen(w, 4) 
for i in g: print(i)