那些遇到过的问题

优化键列表的字典成员资格的性能

Nam*_*man 19 python performance dictionary list python-2.7

我正在尝试编写一个代码,如果列表中存在任何列表元素,则该代码应返回true.这件作品的表现非常重要.我知道如果我找到第一个搜索命中,我可以循环遍历列表并中断.有没有更快或更多的Pythonic方式比下面给出的？

for x in someList:
     if x in someDict:
           return True
return False
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编辑:我正在使用Python 2.7.我的第一个偏好是更快的方法.

Abh*_*jit 38

使用内置任何一个可以在两个循环上具有一些性能优势

any(x in someDict for x in someList)
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但你可能需要衡量你的里程数.如果您的列表和字典仍然非常静态,并且您必须多次执行比较,则可以考虑使用set

someSet = set(someList) 
someDict.viewkeys() & someSet
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注意 Python 3.X默认返回视图而不是序列,所以在使用Python 3.X时它会很简单

someSet = set(someList) 
someDict.keys() & someSet
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在上述两种情况下,您都可以使用bool包装结果以获得布尔结果

bool(someDict.keys() & set(someSet ))
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异端音符

我的好奇心让我变得更好,我计划了所有提议的解决方案.您的原始解决方案似乎更好的性能.这是结果

样本随机生成的输入

def test_data_gen():
    from random import sample
    for i in range(1,5):
        n = 10**i
        population = set(range(1,100000))
        some_list = sample(list(population),n)
        population.difference_update(some_list)
        some_dict = dict(zip(sample(population,n),
                             sample(range(1,100000),n)))
        yield "Population Size of {}".format(n), (some_list, some_dict), {}
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测试引擎

I rewrote the Test Part of the answer as it was messy and the answer was receiving quite a decent attention. I created a timeit compare python module and moved it onto github

The Test Result

Timeit repeated for 10 times
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
======================================
Test Run for Population Size of 10
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.000011  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.000014  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_not_not  |0.000015  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_imap_any         |0.000018  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     5|foo_any              |0.000019  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_ifilter_next     |0.000022  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.000024  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.000047  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 100
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_any      |0.000071  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_nested           |0.000072  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_not_not  |0.000073  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_next     |0.000076  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_imap_any         |0.000082  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.000092  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.000170  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.000638  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 1000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_not_not  |0.000746  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.000746  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_next     |0.000752  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_nested           |0.000771  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     5|foo_set_ashwin       |0.000838  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_imap_any         |0.000842  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |0.000933  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.001702  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 10000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.007195  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_next     |0.007410  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_any      |0.007491  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_not_not  |0.007671  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_set_ashwin       |0.008385  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_imap_any         |0.011327  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |0.011533  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.018313  |some_dict.viewkeys() & set(some_list )
Timeit repeated for 100 times
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
======================================
Test Run for Population Size of 10
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.000098  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.000124  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_not_not  |0.000131  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_imap_any         |0.000142  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     5|foo_ifilter_next     |0.000151  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.000158  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.000186  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.000496  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 100
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_any      |0.000661  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_not_not  |0.000677  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_nested           |0.000683  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_next     |0.000684  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_imap_any         |0.000762  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.000854  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.001291  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.005018  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 1000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_any      |0.007585  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_nested           |0.007713  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     3|foo_set_ashwin       |0.008256  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_not_not  |0.008526  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_any              |0.009422  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_ifilter_next     |0.010259  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     7|foo_imap_any         |0.011414  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.019862  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 10000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_imap_any         |0.082221  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.083573  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_nested           |0.095736  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     4|foo_set_ashwin       |0.103427  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     5|foo_ifilter_next     |0.104589  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     6|foo_ifilter_not_not  |0.117974  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |0.127739  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.208228  |some_dict.viewkeys() & set(some_list )
Timeit repeated for 1000 times
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
======================================
Test Run for Population Size of 10
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.000953  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.001134  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_not_not  |0.001213  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_next     |0.001340  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_imap_any         |0.001407  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.001535  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.002252  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.004701  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 100
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_any      |0.006209  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_next     |0.006411  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_not_not  |0.006657  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_nested           |0.006727  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     5|foo_imap_any         |0.007562  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.008262  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.012260  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.046773  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 1000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_not_not  |0.071888  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_next     |0.072150  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_nested           |0.073382  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_any      |0.075698  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     5|foo_set_ashwin       |0.077367  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_imap_any         |0.090623  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |0.093301  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.177051  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 10000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.701317  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_next     |0.706156  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_any      |0.723368  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_not_not  |0.746650  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_set_ashwin       |0.776704  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_imap_any         |0.832117  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |0.881777  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |1.665962  |some_dict.viewkeys() & set(some_list )
Timeit repeated for 10000 times
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
======================================
Test Run for Population Size of 10
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.010581  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_any      |0.013512  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     3|foo_imap_any         |0.015321  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     4|foo_ifilter_not_not  |0.017680  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     5|foo_ifilter_next     |0.019334  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.026274  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.030881  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.053605  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 100
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_nested           |0.070194  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_not_not  |0.078524  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_any      |0.079499  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     4|foo_imap_any         |0.087349  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     5|foo_ifilter_next     |0.093970  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     6|foo_any              |0.097948  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     7|foo_set_ashwin       |0.130725  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |0.480841  |some_dict.viewkeys() & set(some_list )
======================================
Test Run for Population Size of 1000
======================================
|Rank  |FunctionName         |Result    |Description
+------+---------------------+----------+-----------------------------------------------
|     1|foo_ifilter_any      |0.754491  |any(ifilter(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     2|foo_ifilter_not_not  |0.756253  |not not next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     3|foo_ifilter_next     |0.771382  |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+----------+-----------------------------------------------
|     4|foo_nested           |0.787152  |Original OPs Code
+------+---------------------+----------+-----------------------------------------------
|     5|foo_set_ashwin       |0.818520  |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+----------+-----------------------------------------------
|     6|foo_imap_any         |0.902947  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+----------+-----------------------------------------------
|     7|foo_any              |1.001810  |any(x in some_dict for x in some_list)
+------+---------------------+----------+-----------------------------------------------
|     8|foo_set              |2.012781  |some_dict.viewkeys() & set(some_list )
=======================================
Test Run for Population Size of 10000
=======================================
|Rank  |FunctionName         |Result     |Description
+------+---------------------+-----------+-----------------------------------------------
|     1|foo_imap_any         |10.071469  |any(imap(some_dict.__contains__, some_list))
+------+---------------------+-----------+-----------------------------------------------
|     2|foo_any              |11.127034  |any(x in some_dict for x in some_list)
+------+---------------------+-----------+-----------------------------------------------
|     3|foo_set              |18.881414  |some_dict.viewkeys() & set(some_list )
+------+---------------------+-----------+-----------------------------------------------
|     4|foo_nested           |8.731133   |Original OPs Code
+------+---------------------+-----------+-----------------------------------------------
|     5|foo_ifilter_not_not  |9.019190   |not not next(ifilter(some_dict.__contains__...
+------+---------------------+-----------+-----------------------------------------------
|     6|foo_ifilter_next     |9.189966   |bool(next(ifilter(some_dict.__contains__...
+------+---------------------+-----------+-----------------------------------------------
|     7|foo_set_ashwin       |9.363886   |not set(some_dct).isdisjoint(some_lst)
+------+---------------------+-----------+-----------------------------------------------
|     8|foo_ifilter_any      |9.442759   |any(ifilter(some_dict.__contains__, some_list))
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And a Graphical Comparison from the above referred module

enter image description here enter image description here enter image description here enter image description here

Conclusion

Premature optimization is evil. It is evident that none of the solutions have optimal performance when the test domain varies. Depending on population size and frequency of iteration, performance of solutions varies considerably. The result again speaks out about the fact that in Python, one should ensure that the code should be readable rather than ensuring that the code is either nifty or optimized for performance for certain cases, but then it may not be scalable.

Note There were some doubts on why not using ifilter performs better than the rest

"In Abhit's answer, he timed the different approaches and found that ifilter/next was not the fastest; any idea why this would be the case? "

It is a known fact that in python, there is an overhead when calling C functions, and if the population size is low but the frequency of iteration is high, the accumulation of C function call overhead would slowly show up. As can be seen in the graphs, where population size is low but iteration is high, using ifilter, performance deviates considerably.

  • 除了使答案变得冗长而丰富多彩之外,还有什么能够显示少于10,000次重复的时间？重复次数越少意味着测量结果越多.那些应该从答案中删除(或者至少将最可靠的测量值移到顶部而不是将它们留在最后). (4认同)
  • 而不是`set.intersection`我会使用`set.isdisjoint`:`not set(some_dct).isdisjoint(some_lst)`.Dictviews很慢,因为你在`dict`和list(隐式和显式)上调用`set()`,OTOH`set(some_dct).isdisjoint(some_lst)`将首先转换`some_dict`然后我们循环遍历`some_list`的项目并检查它是否包含在集合中,如果是短路则. (2认同)

Ray*_*ger 10

最干净,最快捷的方法是使用any()和itertools.ifilter():

any(ifilter(someDict.__contains__, someList))
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此代码使用:

  • 绑定方法,someDict.__contains__作为谓词
  • 所述的IFilter() itertool懒惰地扫描中C速度的真实结果
  • 对任何()内置驱动过滤器找到一个匹配发生或返回假如果迭代被耗尽.

您也可以使用itertools.imap()而不是ifilter().

  • 在Abhit的回答中,他定时采用不同的方法,发现ifilter/next不是最快的; 知道为什么会这样吗？ (3认同)
  • 如果速度提高10-20%,我会以最快的方式感兴趣.你能否根据ifilter的具体情况编辑答案？ (2认同)
  • 结论是事先可以知道的.对于短序列,纯python胜出,因为它没有函数调用开销.对于长序列,itertools获胜,因为它没有解释器循环开销(它专门用于解决此问题).您不需要30个时间和图表来了解它的结果.此外,"为什么"更重要的是实际时间(以便知识可以应用于其他地方). (2认同)

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