更快的strptime？ [英] A faster strptime?

问题描述

我有一段代码，可以读取 YYYY-MM-DD格式的大量日期。解析所有这些日期，以便可以增加一，两或三天，然后以相同的格式写回，这会大大降低速度。

I have code which reads vast numbers of dates in 'YYYY-MM-DD' format. Parsing all these dates, so that it can add one, two, or three days then write back in the same format is slowing things down quite considerably.

 3214657   14.330    0.000  103.698    0.000 trade.py:56(effective)
 3218418   34.757    0.000   66.155    0.000 _strptime.py:295(_strptime)

 day = datetime.datetime.strptime(endofdaydate, "%Y-%m-%d").date()

任何建议如何加快速度（或加快速度）？

Any suggestions how to speed it up a bit (or a lot)?

推荐答案

Python 3.7+： fromisoformat（）

自Python 3.7起， datetime 类具有 fromisoformat 方法。应当指出，这也可以应用于以下问题：

Python 3.7+: fromisoformat()

Since Python 3.7, the datetime class has the fromisoformat method. It should be noted that this can also be applied to this question:

显式字符串切片可以使您的性能比正常的 strptime 大约提高9倍，但是您可以获得大约<内置的 fromisoformat 方法使强度提高了90倍！

Explicit string slicing may give you about a 9x increase in performance compared to normal strptime, but you can get about a 90x increase with the built-in fromisoformat method!

%timeit isofmt(datelist)
569 µs ± 8.45 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

%timeit slice2int(datelist)
5.51 ms ± 48.9 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit normalstrptime(datelist)
52.1 ms ± 1.27 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

from datetime import datetime, timedelta
base, n = datetime(2000, 1, 1, 1, 2, 3, 420001), 10000
datelist = [(base + timedelta(days=i)).strftime('%Y-%m-%d') for i in range(n)]

def isofmt(l):
    return list(map(datetime.fromisoformat, l))

def slice2int(l):   
    def slicer(t):
        return datetime(int(t[:4]), int(t[5:7]), int(t[8:10]))
    return list(map(slicer, l))

def normalstrptime(l):
    return [datetime.strptime(t, '%Y-%m-%d') for t in l]

print(isofmt(datelist[0:1]))
print(slice2int(datelist[0:1]))
print(normalstrptime(datelist[0:1]))

# [datetime.datetime(2000, 1, 1, 0, 0)]
# [datetime.datetime(2000, 1, 1, 0, 0)]
# [datetime.datetime(2000, 1, 1, 0, 0)]

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Python 3.8.3rc1 x64 / Win10

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Python 3.8.3rc1 x64 / Win10

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