Python timedelta 对象 - strfdelta 和 deltafstr 函数用于转换 timedelta 字符串

Question

有没有类似于strftime()在datetime对象上工作的方式，在Python中实现strfdelta()和deltafstr()这两个函数？

关于这个问题已经有类似的讨论...

• 如何从简单字符串构造timedelta对象
• 格式化timedelta对象

...但没有一种一致的方法可以在这两种格式之间来回转换。

我想要能够从timedelta转换为string，然后再转换回timedelta。

这个功能的预期用途是用于Hadoop的mapper/reducer过程（mapper脚本的中间delta时间输出，用于输入到reducer脚本中）。

Answer 1

在寻找可以相互转换的函数时，我没有找到合适的，于是自己写了以下两个函数，并把它们放在一个脚本里。这些函数可以在Python v2.6.6中使用，因为这个版本不支持一些更新的功能，比如timedelta.total_seconds()：

#!/usr/bin/python

import re
import sys
import datetime

# String from Date/Time Delta:
#  Takes a datetime.timedelta object, and converts the internal values
#  to a dd:HH:mm:ss:ffffff string, prefixed with "-" if the delta is
#  negative
def strfdelta(tdelta):

    # Handle Negative time deltas
    negativeSymbol = ""
    if tdelta < datetime.timedelta(0):
        negativeSymbol = "-"

    # Convert days to seconds, as individual components could
    # possibly both be negative
    tdSeconds = (tdelta.seconds) + (tdelta.days * 86400)

    # Capture +/- state of seconds for later user with milliseonds calculation
    secsNegMultiplier = 1
    if tdSeconds < 0:
        secsNegMultiplier = -1

    # Extract minutes from seconds
    tdMinutes, tdSeconds = divmod(abs(tdSeconds), 60)

    # Extract hours from minutes
    tdHours, tdMinutes = divmod(tdMinutes, 60)
    # Extract days from hours
    tdDays, tdHours = divmod(tdHours, 24)

    # Convert seconds to microseconds, as individual components 
    # could possibly both be negative
    tdMicroseconds = (tdelta.microseconds) + (tdSeconds * 1000000 * secsNegMultiplier)

    # Get seconds and microsecond components
    tdSeconds, tdMicroseconds = divmod( abs(tdMicroseconds), 1000000)

    return "{negSymbol}{days}:{hours:02d}:{minutes:02d}:{seconds:02d}:{microseconds:06d}".format(
        negSymbol=negativeSymbol,
        days=tdDays,
        hours=tdHours,
        minutes=tdMinutes,
        seconds=tdSeconds,
        microseconds=tdMicroseconds)


# Date/Time delta from string
# Example: -1:23:32:59:020030 (negative sign optional)
def deltafstr(stringDelta):

    # Regular expression to capture status change events, with groups for date/time, 
    #  instrument ID and state
    regex = re.compile("^(-?)(\d{1,6}):([01]?\d|2[0-3]):([0-5][0-9]):([0-5][0-9]):(\d{6})$",re.UNICODE)
    matchObj = regex.search(stringDelta)

    # If this line doesn't match, return None
    if(matchObj is None):
        return None;

    # Debug - Capture date-time from regular expression 
    # for g in range(0, 7):
    #     print "Grp {grp}: ".format(grp=g) + str(matchObj.group(g)) 

    # Get Seconds multiplier (-ve sign at start)
    secsNegMultiplier = 1
    if matchObj.group(1):
        secsNegMultiplier = -1

    # Get time components
    tdDays = int(matchObj.group(2)) * secsNegMultiplier
    tdHours = int(matchObj.group(3)) * secsNegMultiplier
    tdMinutes = int(matchObj.group(4)) * secsNegMultiplier
    tdSeconds = int(matchObj.group(5)) * secsNegMultiplier
    tdMicroseconds = int(matchObj.group(6)) * secsNegMultiplier

    # Prepare return timedelta
    retTimedelta = datetime.timedelta(
        days=tdDays,
        hours=tdHours,
        minutes=tdMinutes,
        seconds=tdSeconds,
        microseconds=tdMicroseconds)

    return retTimedelta;

这里有一些代码，用来测试在这两种格式之间的转换。timedelta对象的构造函数参数可以更改，以测试不同的情况：

# Testing (change the constructor for timedelta to test other cases)
firstDelta = datetime.timedelta(seconds=-1,microseconds=999999, days=-1)
print "--------"
print firstDelta
firstDeltaStr = strfdelta(firstDelta)
print "--------"
print firstDeltaStr;
secondDelta = deltafstr(firstDeltaStr)
print "--------"
print secondDelta
secondDeltaStr = strfdelta(secondDelta)
print "--------"
print secondDelta
print "--------"