如何检查创建一百万个 ndarrays 所花费的时间？

Question

我试图弄清楚创建一百万个（numpy 数组）需要多长时间，并将其与库ndarray所花费的时间进行比较，但出现以下语法错误：listtimeit

File "<timeit-src>", line 2

    [1 2 3 4 5]

       ^

SyntaxError: invalid syntax

这个错误是有道理的，但我什至不知道我该怎么做。

以下是我到目前为止尝试过的代码

import numpy as np

import timeit

arr = [1, 2, 3, 4, 5]

ndarr = np.array([1, 2, 3, 4, 5])

list_time = timeit.timeit(stmt=f'{arr}', number=1000000)

ndarray_time = timeit.timeit(stmt=f'{ndarr}', number=1000000)

print('list takes', list_time, sep=': ')

print('ndarray takes', ndarray_time, sep=': ')

结果list与预期一致，但结果ndarray并非如此。

Answer 1

您可以传递一个可调用对象：list_time = timeit.timeit(stmt=lambda: [1, 2, 3, 4, 5], number=1000000)ndarray_time = timeit.timeit(stmt=lambda: np.array([1, 2, 3, 4, 5]), number=1000000)#lambda: (ndarr := np.array([1, 2, 3, 4, 5])) - (if actual assignment matters...?)您也可以传递一个字符串，但正如此处的评论所暗示的那样，您需要正确设置它：list_time = timeit.timeit(stmt="a = [1, 2, 3, 4, 5]", number=1000000)ndarray_time = timeit.timeit(stmt=lambda: "a = np.array([1, 2, 3, 4, 5])", setup="import numpy as np", number=1000000)

Answer 2

In [628]: arr=[1,2,3,4,5]&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;In [629]: ndarr=np.array([1,2,3,4,5])&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;In [630]: f'{arr}'&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Out[630]: '[1, 2, 3, 4, 5]'In [631]: f'{ndarr}'&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Out[631]: '[1 2 3 4 5]'问题是 while"[1, 2, 3, 4, 5]"是一个可执行表达式，"[1 2 3 4 5]"但不是。很难从现有的表达式创建可执行表达式ndarray- 并非不可能，但您必须努力。在ipython会话中，运行这样的 timeit 测试很简单：In [632]: timeit [1,2,4,5]&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;60.6 ns ± 1.77 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)In [633]: timeit np.array([1,2,4,5])&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;2.22 µs ± 20.7 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)更好repr，看起来更像列表In [635]: f'{repr(ndarr)}'&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Out[635]: 'array([1, 2, 3, 4, 5])'但即使这样也需要调整才能使array零件正确。