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timedelta problem

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  timedelta  problem luofeiyu <elearn2014@gmail.com> - 2014-08-15 10:24 +0800
    Re: timedelta  problem Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-15 03:51 +0000
      Re: timedelta problem Chris Angelico <rosuav@gmail.com> - 2014-08-15 13:59 +1000
      Re: timedelta problem Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-14 22:00 -0600
    Re: timedelta  problem Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-15 07:39 +0000
      Re: timedelta  problem Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-15 08:44 +0000
      Re: timedelta problem Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-15 09:23 -0600
        Re: timedelta problem Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-15 17:43 +0000
          Re: timedelta problem Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-15 12:05 -0600
      Re: timedelta problem Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-08-15 17:29 +0100
    Re: timedelta  problem Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-15 09:36 +0000

#76342 — timedelta problem

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In the python doc , https://docs.python.org/3.4/library/datetime.html

A timedelta 
<https://docs.python.org/3.4/library/datetime.html#datetime.timedelta> 
object represents a duration, the difference between two dates or times.

/class /datetime.timedelta(/days=0/, /seconds=0/, /microseconds=0/, 
/milliseconds=0/, /minutes=0/, /hours=0/, /weeks=0/)

    All arguments are optional and default to 0. Arguments may be
    integers or floats, and may be positive or negative.

    Only /days/, /seconds/ and /microseconds/ are stored internally.

import datetime
t1='Sat, 09 Aug 2014 07:36:46 -0700'
t2='Sat, 09 Aug 2014 07:36:46 +0700'
 >>> datetime.datetime.strptime(t1,"%a, %d %b %Y %H:%M:%S %z")
datetime.datetime(2014, 8, 9, 7, 36, 46, 
tzinfo=datetime.timezone(datetime.timed
elta(-1, 61200)))
 >>> datetime.datetime.strptime(t2,"%a, %d %b %Y %H:%M:%S %z")
datetime.datetime(2014, 8, 9, 7, 36, 46, 
tzinfo=datetime.timezone(datetime.timed
elta(0, 25200)))


problem :

t1 is GMT time   2014  00:36:46
t2 is GMT time   2014  14:36:46

datetime.datetime.strptime  do not give me the right answer.

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#76350

On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:

> import datetime
> t1='Sat, 09 Aug 2014 07:36:46 -0700'
> t2='Sat, 09 Aug 2014 07:36:46 +0700'
> datetime.datetime.strptime(t1,"%a, %d %b %Y %H:%M:%S %z")

Are you sure? When I try this I get:

ValueError: 'z' is a bad directive in format '%a, %d %b %Y %H:%M:%S %z'

> datetime.datetime(2014, 8, 9, 7, 36, 46,
> tzinfo=datetime.timezone(datetime.timedelta(-1, 61200)))

And this:

AttributeError: 'module' object has no attribute 'timezone'

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#76351 — Re: timedelta problem

On Fri, Aug 15, 2014 at 1:51 PM, Denis McMahon <denismfmcmahon@gmail.com> wrote:
> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>
>> import datetime
>> t1='Sat, 09 Aug 2014 07:36:46 -0700'
>> t2='Sat, 09 Aug 2014 07:36:46 +0700'
>> datetime.datetime.strptime(t1,"%a, %d %b %Y %H:%M:%S %z")
>
> Are you sure? When I try this I get:
>
> ValueError: 'z' is a bad directive in format '%a, %d %b %Y %H:%M:%S %z'
>
>> datetime.datetime(2014, 8, 9, 7, 36, 46,
>> tzinfo=datetime.timezone(datetime.timedelta(-1, 61200)))
>
> And this:
>
> AttributeError: 'module' object has no attribute 'timezone'

Both fail as you describe in 2.7, but in 3.4/3.5ish (my 'python3' is a
bit of a mess, but it's something between those two I think), both
work as per the OP's description. You both need to be clearer about
version numbers, I think :) The OP did have a link to docs with 3.4 in
the name, although that isn't proof necessarily.

ChrisA

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#76352 — Re: timedelta problem

[Multipart message — attachments visible in raw view] — view raw

On Thu, Aug 14, 2014 at 9:51 PM, Denis McMahon <denismfmcmahon@gmail.com>
wrote:
>
> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>
> > import datetime
> > t1='Sat, 09 Aug 2014 07:36:46 -0700'
> > t2='Sat, 09 Aug 2014 07:36:46 +0700'
> > datetime.datetime.strptime(t1,"%a, %d %b %Y %H:%M:%S %z")
>
> Are you sure? When I try this I get:
>
> ValueError: 'z' is a bad directive in format '%a, %d %b %Y %H:%M:%S %z'
>
> > datetime.datetime(2014, 8, 9, 7, 36, 46,
> > tzinfo=datetime.timezone(datetime.timedelta(-1, 61200)))
>
> And this:
>
> AttributeError: 'module' object has no attribute 'timezone'

The datetime.timezone class was added in Python 3.2.

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#76355

On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:

On further inspection, it seems that strptime() in 2.7 doesn't handle %z 
at all. In 3.2, it ignores the value it gets, because there's no 
practical way to select the "right" tz string from the offset.

For example, a dictionary of offset minutes to tzstrings looks something 
like this:

{
-720: ['BIT'], 
-660: ['NUT', 'SST'], 
-600: ['CKT', 'HAST', 'HST', 'TAHT'], 
-570: ['MART', 'MIT'], 
-540: ['AKST', 'GAMT', 'GIT', 'HADT'], 
-480: ['AKDT', 'CIST', 'PST'], 
-420: ['MST', 'PDT'], 
-360: ['CST', 'EAST', 'GALT', 'MDT'], 
-300: ['CDT', 'COT', 'CST', 'EASST', 'ECT', 'EST', 'PET'], 
-270: ['VET'], 
-240: ['AMT', 'AST', 'BOT', 'CDT', 'CLT', 'COST', 'ECT', 'EDT', 'FKT', 
'GYT', 'PYT'], 
-210: ['NST', 'NT'], 
-180: ['ADT', 'AMST', 'ART', 'BRT', 'CLST', 'FKST', 'FKST', 'GFT', 'PMST', 
'PYST', 'ROTT', 'SRT', 'UYT'], 
-150: ['NDT'], 
-120: ['FNT', 'GST', 'PMDT', 'UYST'], 
-60: ['AZOST', 'CVT', 'EGT'], 
0: ['GMT', 'UCT', 'UTC', 'WET', 'Z', 'EGST'], 
60: ['BST', 'CET', 'DFT', 'IST', 'MET', 'WAT', 'WEDT', 'WEST'], 
120: ['CAT', 'CEDT', 'CEST', 'EET', 'HAEC', 'IST', 'MEST', 'SAST', 
'WAST'], 
180: ['AST', 'EAT', 'EEDT', 'EEST', 'FET', 'IDT', 'IOT', 'SYOT'], 
210: ['IRST'], 
240: ['AMT', 'AZT', 'GET', 'GST', 'MSK', 'MUT', 'RET', 'SAMT', 'SCT', 
'VOLT'], 
270: ['AFT', 'IRDT'], 
300: ['AMST', 'HMT', 'MAWT', 'MVT', 'ORAT', 'PKT', 'TFT', 'TJT', 'TMT', 
'UZT'], 
330: ['IST', 'SLST'], 
345: ['NPT'], 
360: ['BIOT', 'BST', 'BTT', 'KGT', 'VOST', 'YEKT'], 
390: ['CCT', 'MMT', 'MST'], 
420: ['CXT', 'DAVT', 'HOVT', 'ICT', 'KRAT', 'OMST', 'THA', 'WIT'], 
480: ['ACT', 'AWST', 'BDT', 'CHOT', 'CIT', 'CST', 'CT', 'HKT', 'MST', 
'MYT', 'PST', 'SGT', 'SST', 'ULAT', 'WST'], 
525: ['CWST'], 
540: ['AWDT', 'EIT', 'IRKT', 'JST', 'KST', 'TLT'], 
570: ['ACST', 'CST'], 
600: ['AEST', 'CHUT', 'DDUT', 'EST', 'PGT', 'VLAT', 'YAKT'], 
630: ['ACDT', 'CST', 'LHST'], 
660: ['AEDT', 'KOST', 'LHST', 'MIST', 'NCT', 'PONT', 'SAKT', 'SBT', 
'VUT'], 
690: ['NFT'], 
720: ['FJT', 'GILT', 'MAGT', 'MHT', 'NZST', 'PETT', 'TVT', 'WAKT'], 
765: ['CHAST']
780: ['NZDT', 'PHOT', 'TKT', 'TOT'], 
825: ['CHADT'], 
840: ['LINT'], 
}

I've patched my 2.7 to set a tz string of "UTC[+-]nnnn" from the [+-]nnnn 
%z value.

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#76362

On Fri, 15 Aug 2014 07:39:23 +0000, Denis McMahon wrote:

> I've patched my 2.7 to set a tz string of "UTC[+-]nnnn" from the
> [+-]nnnn %z value.

... but that doesn't do much, because time.struct_time in 2.7 doesn't 
recognise anything that strptime passes in as a tz at all, as it expects 
the dst flag in that position and seems to have no concept of tz at all.

So in 2.7 you can probably forget any question of reading in tz info with 
datetime.strptime().

See another reply to the OP regarding Python 3.2

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#76374 — Re: timedelta problem

On Fri, Aug 15, 2014 at 1:39 AM, Denis McMahon <denismfmcmahon@gmail.com> wrote:
> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>
> On further inspection, it seems that strptime() in 2.7 doesn't handle %z
> at all. In 3.2, it ignores the value it gets, because there's no
> practical way to select the "right" tz string from the offset.

I'm not sure when %z was added, but it's worth noting that it doesn't
seem to be documented earlier than 3.3.

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#76379 — Re: timedelta problem

On Fri, 15 Aug 2014 09:23:02 -0600, Ian Kelly wrote:

> On Fri, Aug 15, 2014 at 1:39 AM, Denis McMahon
> <denismfmcmahon@gmail.com> wrote:
>> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>>
>> On further inspection, it seems that strptime() in 2.7 doesn't handle
>> %z at all. In 3.2, it ignores the value it gets, because there's no
>> practical way to select the "right" tz string from the offset.
> 
> I'm not sure when %z was added, but it's worth noting that it doesn't
> seem to be documented earlier than 3.3.

There may be some confusion because %z is in the table of strftime and 
strptime format chars on the 2.7.8 docs at

https://docs.python.org/2/library/datetime.html#strftime-and-strptime-
behavior

but I suspect it's only applicable to strftime in that release.

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#76380 — Re: timedelta problem

On Fri, Aug 15, 2014 at 11:43 AM, Denis McMahon
<denismfmcmahon@gmail.com> wrote:
> On Fri, 15 Aug 2014 09:23:02 -0600, Ian Kelly wrote:
>
>> On Fri, Aug 15, 2014 at 1:39 AM, Denis McMahon
>> <denismfmcmahon@gmail.com> wrote:
>>> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>>>
>>> On further inspection, it seems that strptime() in 2.7 doesn't handle
>>> %z at all. In 3.2, it ignores the value it gets, because there's no
>>> practical way to select the "right" tz string from the offset.
>>
>> I'm not sure when %z was added, but it's worth noting that it doesn't
>> seem to be documented earlier than 3.3.
>
> There may be some confusion because %z is in the table of strftime and
> strptime format chars on the 2.7.8 docs at
>
> https://docs.python.org/2/library/datetime.html#strftime-and-strptime-
> behavior
>
> but I suspect it's only applicable to strftime in that release.

Ah, interesting. I was looking at the time.strptime docs. I
incorrectly assumed that since help(datetime.strptime) defers to
help(time.strptime), the docs would also.

I note it says that "datetime.strptime(date_string, format) is
equivalent to datetime(*(time.strptime(date_string, format)[0:6]))",
but clearly that's not the case when the format includes %z.

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#76375 — Re: timedelta problem

On 15/08/2014 16:23, Ian Kelly wrote:
> On Fri, Aug 15, 2014 at 1:39 AM, Denis McMahon <denismfmcmahon@gmail.com> wrote:
>> On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:
>>
>> On further inspection, it seems that strptime() in 2.7 doesn't handle %z
>> at all. In 3.2, it ignores the value it gets, because there's no
>> practical way to select the "right" tz string from the offset.
>
> I'm not sure when %z was added, but it's worth noting that it doesn't
> seem to be documented earlier than 3.3.
>

Looks like this http://bugs.python.org/issue16667

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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#76364

On Fri, 15 Aug 2014 10:24:47 +0800, luofeiyu wrote:

> problem :
> 
> t1 is GMT time   2014  00:36:46 t2 is GMT time   2014  14:36:46
> 
> datetime.datetime.strptime  do not give me the right answer.

As far as I can tell from running the following, it all seems to work as 
expected in python 3.2 (and hence I expect in 3.4). If the expected 
output doesn't match yours, it would be interesting to see what your 
output is. If the expected output does match yours, and you think it's 
wrong, it would be interesting to know which bits you think are wrong and 
why you think they are wrong, because having a fair bit of the night 
looking at this, it all looks good to me.

#!/usr/bin/python3

from datetime import tzinfo, timedelta, datetime, timezone

# define timedelta based timezones

UTCm7 = timezone(timedelta(0,-7*3600),"UTC-07:00")
UTCp7 = timezone(timedelta(0,+7*3600),"UTC+07:00")
UTC  = timezone(timedelta(0),        "UTC+00:00")

# some timestrings

t1 = 'Sat, 09 Aug 2014 07:36:46 -0700'
t2 = 'Sat, 09 Aug 2014 07:36:46 +0700'
t3 = 'Sat, 09 Aug 2014 07:36:46 +0000'

# make some datetime objects
# these are both utc -7

a1 = datetime.strptime(t1,"%a, %d %b %Y %H:%M:%S %z")
b1 = datetime(2014, 8, 9, 7, 36, 46, tzinfo = UTCm7)

# these are both utc +7

a2 = datetime.strptime(t2,"%a, %d %b %Y %H:%M:%S %z")
b2 = datetime(2014, 8, 9, 7, 36, 46, tzinfo = UTCp7)

# these are both utc

a3 = datetime.strptime(t3,"%a, %d %b %Y %H:%M:%S %z")
b3 = datetime(2014, 8, 9, 7, 36, 46, tzinfo = UTC)

# print them out as stored

print( "UTC -7:" )
print( t1 )
print( a1 )
print( b1 )

print( "UTC +7:" )
print( t2 )
print( a2 )
print( b2 )

print( "UTC:" )
print( t3 )
print( a3 )
print( b3 )

# print them out converted to UTC

print( "UTC -7 as UTC:" )
print( a1.astimezone( UTC ) )
print( b1.astimezone( UTC ) )

print( "UTC +7 as UTC:" )
print( a2.astimezone( UTC ) )
print( b2.astimezone( UTC ) )

print( "UTC as UTC:" )
print( a3.astimezone( UTC ) )
print( b3.astimezone( UTC ) )

# expected output

"""
UTC -7:
Sat, 09 Aug 2014 07:36:46 -0700
2014-08-09 07:36:46-07:00
2014-08-09 07:36:46-07:00
UTC +7:
Sat, 09 Aug 2014 07:36:46 +0700
2014-08-09 07:36:46+07:00
2014-08-09 07:36:46+07:00
UTC:
Sat, 09 Aug 2014 07:36:46 +0000
2014-08-09 07:36:46+00:00
2014-08-09 07:36:46+00:00
UTC -7 as UTC:
2014-08-09 14:36:46+00:00
2014-08-09 14:36:46+00:00
UTC +7 as UTC:
2014-08-09 00:36:46+00:00
2014-08-09 00:36:46+00:00
UTC as UTC:
2014-08-09 07:36:46+00:00
2014-08-09 07:36:46+00:00
"""

-- 
Denis McMahon, denismfmcmahon@gmail.com

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