Date Comparison and Manipulation Functions?

**Paul Rudin** · Aug 24 '08, 05:25 PM

Re: Date Comparison and Manipulation Functions?

"W. eWatson" <notvalid2@sbcg lobal.netwrites :

Are there some date and time comparison functions that would compare, say,
>
Is 10/05/05 later than 09/22/02? (or 02/09/22 format, yy/mm/dd)
Is 02/11/07 the same as 02/11/07?
>
Is 14:05:18 after 22:02:51? (24 hour day is fine)
>
How about the date after 02/28/04 is 02/29/04, or the date after
09/30/08 is 10/01/08?
>
How about is 03/03/04 20:10:08 after 03/07/03 14:00:00? Probably the
others above will suffice.

datetime — Basic date and time types

http://docs.python.org/lib/module-datetime.html

Source code: Lib/datetime.py The datetime module supplies classes for manipulating dates and times. While date and time arithmetic is supported, the focus of the implementation is on efficient attr...

**zuul@ferg.org** · Aug 25 '08, 03:35 AM

Re: Date Comparison and Manipulation Functions?

check out Pyfdate: http://www.ferg.org/pyfdate

from pyfdate import *

t = Time().add(hour s=14)
print "It is now", t.wdt

datestring1 = "2005/10/05" #year,month,day
datestring2 = "2002/09/22" #year,month,day
datestring3 = "2007/11/11" #year,month,day

year,month,day = numsplit(datest ring1) # split into integers
t1 = Time(year,month ,day)
for datestring in (datestring2,da testring1,dates tring3):
year,month,day = numsplit(datest ring)
t2 = Time(year,month ,day)

if t1 t2:
print t1.isodate, "is later than ", t2.isodate
elif t1 == t2:
print t1.isodate, "is the same as ", t2.isodate
elif t1 < t2:
print t1.isodate, "is earlier than", t2.isodate

print

t1 = Time(2000,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2001,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2004,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d

print
datestring1 = "2005/10/05 20:10:08"
datestring2 = "2005/10/05 20:10:06"
datestring3 = "2005/10/05 20:10:09"

t1 = Time(*numsplit( datestring1))
for datestring in (datestring2,da testring1,dates tring3):
t2 = Time(*numsplit( datestring))

if t1 t2:
print t1.d, t1.civiltime2, "is later than ", t2.d, t2.civiltime2
elif t1 == t2:
print t1.d, t1.civiltime2, "is the same as ", t2.d, t2.civiltime2
elif t1 < t2:
print t1.d, t1.civiltime2, "is earlier than", t2.d, t2.civiltime2

**W. eWatson** · Aug 26 '08, 01:05 AM

Re: Date Comparison and Manipulation Functions?

zuul@ferg.org wrote:

check out Pyfdate: http://www.ferg.org/pyfdate
>
from pyfdate import *
>
t = Time().add(hour s=14)
print "It is now", t.wdt
>
datestring1 = "2005/10/05" #year,month,day
datestring2 = "2002/09/22" #year,month,day
datestring3 = "2007/11/11" #year,month,day
>
year,month,day = numsplit(datest ring1) # split into integers
t1 = Time(year,month ,day)
for datestring in (datestring2,da testring1,dates tring3):
year,month,day = numsplit(datest ring)
t2 = Time(year,month ,day)
>
if t1 t2:
print t1.isodate, "is later than ", t2.isodate
elif t1 == t2:
print t1.isodate, "is the same as ", t2.isodate
elif t1 < t2:
print t1.isodate, "is earlier than", t2.isodate
>
print
>
t1 = Time(2000,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2001,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2004,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
>
print
datestring1 = "2005/10/05 20:10:08"
datestring2 = "2005/10/05 20:10:06"
datestring3 = "2005/10/05 20:10:09"
>
t1 = Time(*numsplit( datestring1))
for datestring in (datestring2,da testring1,dates tring3):
t2 = Time(*numsplit( datestring))
>
if t1 t2:
print t1.d, t1.civiltime2, "is later than ", t2.d, t2.civiltime2
elif t1 == t2:
print t1.d, t1.civiltime2, "is the same as ", t2.d, t2.civiltime2
elif t1 < t2:
print t1.d, t1.civiltime2, "is earlier than", t2.d, t2.civiltime2

It looks good. Thanks.

--
Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: <www.speckledwi thstars.net/>

**W. eWatson** · Aug 27 '08, 12:25 AM

Re: Date Comparison and Manipulation Functions?

zuul@ferg.org wrote:

check out Pyfdate: http://www.ferg.org/pyfdate
>
from pyfdate import *
>
t = Time().add(hour s=14)
print "It is now", t.wdt
>
datestring1 = "2005/10/05" #year,month,day
datestring2 = "2002/09/22" #year,month,day
datestring3 = "2007/11/11" #year,month,day
>
year,month,day = numsplit(datest ring1) # split into integers
t1 = Time(year,month ,day)
for datestring in (datestring2,da testring1,dates tring3):
year,month,day = numsplit(datest ring)
t2 = Time(year,month ,day)
>
if t1 t2:
print t1.isodate, "is later than ", t2.isodate
elif t1 == t2:
print t1.isodate, "is the same as ", t2.isodate
elif t1 < t2:
print t1.isodate, "is earlier than", t2.isodate
>
print
>
t1 = Time(2000,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2001,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
t1 = Time(2004,2,28)
print "The date after", t1.d, "is", t1.plus(day=1). d
>
print
datestring1 = "2005/10/05 20:10:08"
datestring2 = "2005/10/05 20:10:06"
datestring3 = "2005/10/05 20:10:09"
>
t1 = Time(*numsplit( datestring1))
for datestring in (datestring2,da testring1,dates tring3):
t2 = Time(*numsplit( datestring))
>
if t1 t2:
print t1.d, t1.civiltime2, "is later than ", t2.d, t2.civiltime2
elif t1 == t2:
print t1.d, t1.civiltime2, "is the same as ", t2.d, t2.civiltime2
elif t1 < t2:
print t1.d, t1.civiltime2, "is earlier than", t2.d, t2.civiltime2

I'm using IDLE for Python 2.4, and put pfydate distribution in
C:\Python24\Lib \site-packages\pfydat e, as required by the
<ttp://www.ferg.org/pyfdate/download.htmlpa ge.
How to install pyfdate.

Save pyfdate.py into your PythonNN/Lib/site-packages directory.
I copied it into C:\Python24\Lib \site-packages\pfydat e

Execution in IDLE produced:
---------------------------------
Traceback (most recent call last):
File
"C:\Sandia_Mete ors\Improved_Se ntinel\Sentinel _Playground\dat e_example.py",
line 1, in ?
from pyfdate import *
ImportError: No module named pyfdate
---------------------------------
Looking in the Path Browser, I don't see pyfdate. I see PIL package and
scipy package.

Comments?

--
Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: <www.speckledwi thstars.net/>

**John Machin** · Aug 27 '08, 12:55 AM

Re: Date Comparison and Manipulation Functions?

On Aug 27, 10:21 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

>
I'm using IDLE for Python 2.4, and put pfydate distribution in
C:\Python24\Lib \site-packages\pfydat e, as required by the
<ttp://www.ferg.org/pyfdate/download.htmlpa ge.
How to install pyfdate.
>
Save pyfdate.py into your PythonNN/Lib/site-packages directory.
I copied it into C:\Python24\Lib \site-packages\pfydat e

If that means that you ended up with
C:\Python24\Lib \site-packages\pfydat e\pyfdate.py
then you have *not* followed the instructions "Save pyfdate.py into
your PythonNN/Lib/site-packages directory".
You need to end up with
C:\Python24\Lib \site-packages\pyfdat e.py

If in doubt, get to a command prompt and type
dir C:\Python24\Lib \site-packages\pfydat e*
and tell us what you see.

>
Execution in IDLE produced:
---------------------------------
Traceback (most recent call last):
File
"C:\Sandia_Mete ors\Improved_Se ntinel\Sentinel _Playground\dat e_example.py",
line 1, in ?
from pyfdate import *
ImportError: No module named pyfdate
---------------------------------
Looking in the Path Browser, I don't see pyfdate. I see PIL package and
scipy package.

**W. eWatson** · Aug 27 '08, 01:35 AM

Re: Date Comparison and Manipulation Functions?

John Machin wrote:

On Aug 27, 10:21 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

>I'm using IDLE for Python 2.4, and put pfydate distribution in
>C:\Python24\Li b\site-packages\pfydat e, as required by the
><ttp://www.ferg.org/pyfdate/download.htmlpa ge.
>How to install pyfdate.
>>
> Save pyfdate.py into your PythonNN/Lib/site-packages directory.
>I copied it into C:\Python24\Lib \site-packages\pfydat e

>
If that means that you ended up with
C:\Python24\Lib \site-packages\pfydat e\pyfdate.py
then you have *not* followed the instructions "Save pyfdate.py into
your PythonNN/Lib/site-packages directory".
You need to end up with
C:\Python24\Lib \site-packages\pyfdat e.py

None of the folders in C:\Python24\Lib \site-packages\ have py as a suffix
(as seen either by the IDLE path browser or XP). My folder is exactly
C:\Python24\Lib \site-packages\pfydat e in XP and it contains about 12 py files.
There are exactly three folders under
C:\Python24\Lib \site-packages\ according to the IDLE path browser. This does
not agree with XP, which has:
Numeric
pfydate
scipy
numpy
PIL

>
If in doubt, get to a command prompt and type
dir C:\Python24\Lib \site-packages\pfydat e*
and tell us what you see.
>

>Execution in IDLE produced:
>---------------------------------
>Traceback (most recent call last):
> File
>"C:\Sandia_Met eors\Improved_S entinel\Sentine l_Playground\da te_example.py",
>line 1, in ?
> from pyfdate import *
>ImportError: No module named pyfdate
>---------------------------------
>Looking in the Path Browser, I don't see pyfdate. I see PIL package and
>scipy package.

--
Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: <www.speckledwi thstars.net/>

**John Machin** · Aug 27 '08, 08:05 AM

Re: Date Comparison and Manipulation Functions?

On Aug 27, 11:24 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

John Machin wrote:

On Aug 27, 10:21 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

I'm using IDLE for Python 2.4, and put pfydate distribution in
C:\Python24\Lib \site-packages\pfydat e, as required by the
<ttp://www.ferg.org/pyfdate/download.htmlpa ge.
How to install pyfdate.

>

Save pyfdate.py into your PythonNN/Lib/site-packages directory.
I copied it into C:\Python24\Lib \site-packages\pfydat e

>

If that means that you ended up with
C:\Python24\Lib \site-packages\pfydat e\pyfdate.py
then you have *not* followed the instructions "Save pyfdate.py into
your PythonNN/Lib/site-packages directory".
You need to end up with
C:\Python24\Lib \site-packages\pyfdat e.py

>
None of the folders in C:\Python24\Lib \site-packages\ have py as a suffix
(as seen either by the IDLE path browser or XP). My folder is exactly
C:\Python24\Lib \site-packages\pfydat e in XP and it contains about 12 py files.
There are exactly three folders under
C:\Python24\Lib \site-packages\ according to the IDLE path browser. This does
not agree with XP, which has:
Numeric
pfydate
scipy
numpy
PIL

(1) "pfydate" != "pyfdate"
(2) The instructions say to put pyfdate.py [that's *ONE* file, not 12
files] in the ..../site-packages folder, *not* a sub-folder

**W. eWatson** · Aug 27 '08, 09:15 AM

Re: Date Comparison and Manipulation Functions?

John Machin wrote:

On Aug 27, 11:24 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

>John Machin wrote:

>>On Aug 27, 10:21 am, "W. eWatson" <notval...@sbcg lobal.netwrote:
>>>I'm using IDLE for Python 2.4, and put pfydate distribution in
>>>C:\Python24\ Lib\site-packages\pfydat e, as required by the
>>><ttp://www.ferg.org/pyfdate/download.htmlpa ge.
>>>How to install pyfdate.
>>> Save pyfdate.py into your PythonNN/Lib/site-packages directory.
>>>I copied it into C:\Python24\Lib \site-packages\pfydat e
>>If that means that you ended up with
>> C:\Python24\Lib \site-packages\pfydat e\pyfdate.py
>>then you have *not* followed the instructions "Save pyfdate.py into
>>your PythonNN/Lib/site-packages directory".
>>You need to end up with
>> C:\Python24\Lib \site-packages\pyfdat e.py

>None of the folders in C:\Python24\Lib \site-packages\ have py as a suffix
>(as seen either by the IDLE path browser or XP). My folder is exactly
>C:\Python24\Li b\site-packages\pfydat e in XP and it contains about 12 py files.
>There are exactly three folders under
>C:\Python24\Li b\site-packages\ according to the IDLE path browser. This does
>not agree with XP, which has:
>Numeric
>pfydate
>scipy
>numpy
>PIL

>
(1) "pfydate" != "pyfdate"

typo

(2) The instructions say to put pyfdate.py [that's *ONE* file, not 12
files] in the ..../site-packages folder, *not* a sub-folder
>

Got it. Ah, I see upon closer inspection the other files are just
international versions. Thanks. It works.

--
Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

Web Page: <www.speckledwi thstars.net/>

**W. eWatson** · Aug 29 '08, 04:35 PM

Re: Date Comparison and Manipulation Functions?

I just tried the following code, and got an unexpected result.

from pyfdate import *
t = Time()

ts = Time(2008, 8, 29,15,20,7)
tnew = ts.plus(months= 6)
print "new date: ", tnew

Result:
new date: 2009-02-28 15:20:07

I believe that should be April 1, 2009. If I use months = 1 and day =31, I
get Sept. 30, 2008 and not Oct. 1, 2008. Is there a way to get around this?

--
W. Watson
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

**John Machin** · Aug 29 '08, 11:35 PM

Re: Date Comparison and Manipulation Functions?

On Aug 30, 2:32 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

I just tried the following code, and got an unexpected result.
>
from pyfdate import *
t = Time()
>
ts = Time(2008, 8, 29,15,20,7)
tnew = ts.plus(months= 6)
print "new date: ", tnew
>
Result:
new date: 2009-02-28 15:20:07
>
I believe that should be April 1, 2009.

Presuming that we are talking about the Gregorian calendar, and not
one of your own invention, you are (one trusts) alone in that belief.
There are SEVEN whole months and a bit between August 29, 2008 and
April 1, 2009. Count the months: Sep, Oct, Nov, Dec, Jan, Feb, Mar.

If I use months = 1 and day =31, I
get Sept. 30, 2008 and not Oct. 1, 2008. Is there a way to get around this?

Because the number of days in a month is not constant, adding a number
of months to a date is capable of more than one interpretation. Most
folk are happy with adding the months on and then ensuring that the
day is not later than the last day of the resultant (year, month)
combination -- this is what the pyfdate routine appears to be doing.
However there are some interesting ideas floating around e.g. IIRC an
eminent personage once asserted in this newsgroup that adding 1 month
to 31 Jan in a non-leap year should produce 3 Mar.

There is also the general question with date intervals of whether the
first day is included in the calculation or not. E.g. work on Monday,
Tuesday, Wednesday: that's 3 days service. Put money into the bank on
Monday, withdraw it on Wednesday: that's likely to attract 2 days
interest.

One needs to understand exactly what calculation is required, and
exactly what calculation is provided by the software that is proposed
to be used.

HTH,

John

**W. eWatson** · Aug 30 '08, 12:45 AM

Re: Date Comparison and Manipulation Functions?

John Machin wrote:

On Aug 30, 2:32 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

>I just tried the following code, and got an unexpected result.
>>
>from pyfdate import *
>t = Time()
>>
>ts = Time(2008, 8, 29,15,20,7)
>tnew = ts.plus(months= 6)
>print "new date: ", tnew
>>
>Result:
>new date: 2009-02-28 15:20:07
>>
>I believe that should be April 1, 2009.

>
Presuming that we are talking about the Gregorian calendar, and not
one of your own invention, you are (one trusts) alone in that belief.
There are SEVEN whole months and a bit between August 29, 2008 and
April 1, 2009. Count the months: Sep, Oct, Nov, Dec, Jan, Feb, Mar.
>

>If I use months = 1 and day =31, I
>get Sept. 30, 2008 and not Oct. 1, 2008. Is there a way to get around this?

>
Because the number of days in a month is not constant, adding a number
of months to a date is capable of more than one interpretation. Most
folk are happy with adding the months on and then ensuring that the
day is not later than the last day of the resultant (year, month)
combination -- this is what the pyfdate routine appears to be doing.
However there are some interesting ideas floating around e.g. IIRC an
eminent personage once asserted in this newsgroup that adding 1 month
to 31 Jan in a non-leap year should produce 3 Mar.
>
There is also the general question with date intervals of whether the
first day is included in the calculation or not. E.g. work on Monday,
Tuesday, Wednesday: that's 3 days service. Put money into the bank on
Monday, withdraw it on Wednesday: that's likely to attract 2 days
interest.
>
One needs to understand exactly what calculation is required, and
exactly what calculation is provided by the software that is proposed
to be used.
>
HTH,
>
John

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.) Or:

True calendar period: August 25 to Oct. 5
Recorded calendar period: July 25 to Sept. 5 (roughly 5)

A second function is to correct the time stamp for drift in the clock. For
this, I'm expecting the user knows the daily drift, +/-, in seconds of the
clock. When he decides, for example, that he's let the clock drift for more
than, say, 120 seconds, he may want to adjust the time stamp for all files
collected since the last time he set the clock properly. About the best
anyone can hope for is that the data is accurate to within 4 to 5 seconds,
so over periods of say a month between adjustments this should be OK. The
computers used do not have time data other than that provided by the h/w
clock on the computer. This method is not meant to be a cure all, just to
get the time stamp within a reasonable value. Personally, I reset the time
about every 2-3 weeks. Problems that arise here are associated with working
near midnight. Again, it's possible to set some time or date component
incorrectly each time one needs to get drift under control.

The OSes involved can be Win XP, Win 2000, or even older Win OSes, varieties
of Apple and Linux. I don't want to go below the level of the simple h/w
clock a typical user might have access to through the OS s/w user interface.
However, I do not need to get into OS details to solve the above problems.

There are of course times when a mistaken setting is caught early, so the
adjustment becomes easy. Suppose the day is taken as May 3 on May 5, and two
days later the mistake is noticed. Changing the date for these files is
pretty easy (with the program).

Well, back to the drawing board for awhile to see how this plays against
pyfdate.

--
W. Watson
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

**John Machin** · Aug 30 '08, 02:25 AM

Re: Date Comparison and Manipulation Functions?

On Aug 30, 10:41 am, "W. eWatson" <notval...@sbcg lobal.netwrote:

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(m onths=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_da te = recorded_date.p lus(days=D)

HTH,
John

**W. eWatson** · Aug 30 '08, 10:35 AM

Re: Date Comparison and Manipulation Functions?

John Machin wrote:

On Aug 30, 10:41 am, "W. eWatson" <notval...@sbcg lobal.netwrote:
>

>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_hhmms s.) 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(m onths=6).

Really? It opened new insights for me. The example above is not the only
correction I need to deal with. Further, the author is likely to soon
clarify some of the date rules in the tutorial that were not obvious or
mentioned there.

>
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_da te = recorded_date.p lus(days=D)
>
HTH,
John
>

--
W. Watson
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

**W. eWatson** · Aug 30 '08, 05:35 PM

Re: Date Comparison and Manipulation Functions?

W. eWatson wrote:

John Machin wrote:

>On Aug 30, 10:41 am, "W. eWatson" <notval...@sbcg lobal.netwrote:
>>

>>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_hhmm ss.) 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(m onths=6).

Really? It opened new insights for me. The example above is not the only
correction I need to deal with. Further, the author is likely to soon
clarify some of the date rules in the tutorial that were not obvious or
mentioned there.

>>
>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_da te = recorded_date.p lus(days=D)
>>
>HTH,
>John
>>

>
>

Strange how my post got hooked into this side spur. I'll re-post.

--
W. Watson
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet