Date Comparison and Manipulation Functions?

Hendrik van Rooyen mail at microcorp.co.za
Sat Aug 30 22:57:46 CEST 2008


John Machin <sj..con.net> wrote:

>On Aug 30, 10:41 am, "W. eWatson" <notval....cglobal.net> wrote:
>
>> What I'm trying to do is adjust date-time stamped file names for date and
>> time errors. The software program collects through a period that roughly
>> coincides with night hours every day and according to the OS clock. It
>> sometimes happens that a user sets the clock to the wrong day or hour,
>> possibly both. Possibly even the month or year. I'm trying to allow a user
>> the opportunity to repair the problem. (Date-time stamp part of the name is
>> yyyymmdd_hhmmss.) Correcting the date needs to be done easily and
>> accurately. For example, if on August 25, he mistakenly sets the date to
>> July 25, and discovers this problem on the real Oct. 5, he should be able to
>> shift all dates from July 25 through Sept. 5 to Aug. 25 through early Oct.,
>> allowing for day oddities in a month during the period. (I hope I got those
>> dates right; otherwise, I think you get the idea. In other words, he needs
>> to shift about 40 days of data to the correct dates.)
>
>... all of which is absolutely nothing to do with your surprise at the
>result of whatever.plus(months=6).
>
>So for some period from recorded date X to recorded date Y, the
>recorded dates of out of kilter by D days. X = Jul 25 2008, Y Sep 5
>2008, and D is 31 (days from Jul 25 to Aug 25). All you have to do is
>(pseudocode):
>
>if X <= recorded_date <= Y:
    >new_recorded_date  = recorded_date.plus(days=D)
>

This will work nicely for negative values of D.
The case of positive D values is more of a toffee:

Its Wednesday and I make some observations.
Its Thursday and I "fix" my clock - system thinks its Wednesday again.
I make some observations - Either overwriting or adding to the
original Wednesdays stuff.
Its Friday and I spot the error - my D value is 1 day.
I need to split the "Wednesday" file into two bits, if I can,
and apply the correction to the second half, else I will have
a gap for Wednesday.

Depending on how the logging is done, it may be an unchewable toffee.

- Hendrik






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