使matplotlib的date2num和num2date完美的反转 [英] Making matplotlib's date2num and num2date perfect inverses

问题描述

我正在尝试编写一个函数， plottm 和 unixtm ，它们之间来回转换正常的unix时间（自1970-01-01以来的秒）和Matplotlib的日期表示（从-1BC的最后一天起的天数或某事，浮点数）。

I'm trying to write a pair of functions, plottm and unixtm, which convert back and forth between normal unix time (seconds since 1970-01-01) and Matplotlib's date representation (days since the last day of -1BC or something, a float).

如果 plottm 和 unixtm 是正确的反转，那么这段代码将打印相同的日期/时间两次：

If plottm and unixtm were proper inverses then this code would print the same date/time twice:

import time, datetime
import matplotlib.dates as dt

# Convert a unix time u to plot time p, and vice versa
def plottm(u): return dt.date2num(datetime.datetime.fromtimestamp(u))
def unixtm(p): return time.mktime(dt.num2date(p).timetuple())

u = 1270000000
print datetime.datetime.fromtimestamp(u), "-->", \
      datetime.datetime.fromtimestamp(unixtm(plottm(u)))

唉，这是一个小时（只发生在一些时间戳，否则我' d插入一个偏移量，并完成w

Alas, it's off by an hour (which only happens for some timestamps, otherwise I'd insert an offset and be done with it).

可能相关： Localtime的问题

更新：与Matplotlib不兼容的相关问题：将unixtime转换为datetime对象，然后再次（成对的时间转换函数）

UPDATE: Related question that isn't specific to Matplotlib: Convert a unixtime to a datetime object and back again (pair of time conversion functions that are inverses)

推荐答案

有 matplotlib.dates.epoch2num（）/ num2epoch函数完全相同：

from datetime import datetime, timedelta
import matplotlib.dates as mpl_dt

matplotlib_epoch = datetime(1, 1, 1)  # utc
posix_epoch = datetime(1970, 1, 1)  # utc
DAY = 86400  # seconds


def plottm(u):
    """posix timestamp -> plot time"""
    td = (datetime.utcfromtimestamp(u) - matplotlib_epoch)
    return td.days + 1 + (1000000 * td.seconds + td.microseconds) / 1e6 / DAY


def unixtm(p):
    """plot time -> posix timestamp"""
    td = timedelta(days=p-1)
    return (matplotlib_epoch + td - posix_epoch).total_seconds()


def main():
    f = datetime.utcfromtimestamp
    u = 1270000000.1234567890
    print(f(u))
    print(mpl_dt.epoch2num(u))
    print(plottm(u))
    print(f(mpl_dt.num2epoch(mpl_dt.epoch2num(u))))
    print(f(mpl_dt.num2epoch(plottm(u))))
    print(f(unixtm(mpl_dt.epoch2num(u))))
    print(f(unixtm(plottm(u))))

    assert abs(mpl_dt.epoch2num(u) - plottm(u)) < 1e-5

    p = 86401.234567890 / DAY
    print(f(mpl_dt.num2epoch(p)))
    print(f(unixtm(p)))
    assert abs(mpl_dt.num2epoch(p) - unixtm(p)) < 1e-5

main()

输出

Output

2010-03-31 01:46:40.123457
733862.074076
733862.074076
2010-03-31 01:46:40.123453
2010-03-31 01:46:40.123453
2010-03-31 01:46:40.123453
2010-03-31 01:46:40.123453
0001-01-01 00:00:01.234566
0001-01-01 00:00:01.234566

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