例如，我们可以在生成器中使用递归定义斐波那契序列：

from itertools import pairwise

def fibs():
    yield 0
    yield 1
    yield from map(sum, pairwise(fibs()))

for index, result in enumerate(fibs()):
    print(index, result)

如果我们尝试运行它，它会在索引为1025时放弃，在递归深度超过错误下被粉碎。下面我复制了输出的结尾：

1024 4506699633677819813104383235728886049367860596218604830803023149600030645708721396248792609141030396244873266580345011219530209367425581019871067646094200262285202346655868899711089246778413354004103631553925405243
1025 7291993184377412737043195648396979558721167948342308637716205818587400148912186579874409368754354848994831816250311893410648104792440789475340471377366852420526027975140687031196633477605718294523235826853392138525
Traceback (most recent call last):
  File "/home/user/Área de Trabalho/fibs1.py", line 6, in fibs
    yield from map(sum, pairwise(fibs()))
  File "/home/user/Área de Trabalho/fibs1.py", line 6, in fibs
    yield from map(sum, pairwise(fibs()))
  File "/home/user/Área de Trabalho/fibs1.py", line 6, in fibs
    yield from map(sum, pairwise(fibs()))
  [Previous line repeated 997 more times]
RecursionError: maximum recursion depth exceeded while calling a Python object

现在我们可以尝试通过用生成器表达式替换map来更改它，以使其更Pythonic：

from itertools import pairwise

def fibs():
    yield 0
    yield 1
    yield from (sum(pair) for pair in pairwise(fibs()))

for index, result in enumerate(fibs()):
    print(index, result)

现在问题是，这个版本的运行时间只有第一个版本的一半，内爆深度仅为513，错误消息要大得多，同时它还返回最大递归深度超过错误：

512 44893845313309942978077298160660626646181883623886239791269694466661322268805744081870933775586567858979269
513 72639767602615659833415769076743441675530755653534070653184546540063470576806357692953027861477736726533858
Traceback (most recent call last):
  File "/home/user/Área de Trabalho/fibs2.py", line 6, in <genexpr>
    yield from (sum(pair) for pair in pairwise(fibs()))
  File "/home/user/Área de Trabalho/fibs2.py", line 6, in fibs
    (... this repeats a lot, exceeds maximum character limit in SO)
    yield from (sum(pair) for pair in pairwise(fibs()))
  File "/home/user/Área de Trabalho/fibs2.py", line 6, in fibs
    yield from (sum(pair) for pair in pairwise(fibs()))
RecursionError: maximum recursion depth exceeded while calling a Python object

所以我问，为什么有区别？

我在玩fibonacci Joel Grus在他的博客中发布的类似haskell的实现时注意到了这个问题，但将其更改为使用python 3.10发布时在itertools模块中引入的成对。这样就需要单个导入（成对），而不是三个导入（add， islice，tec）和一个辅助函数定义（尾巴）。