strptime in 2.3.3

[Holger Joukl]

> Andy writes:
> Folks,
>
> I am parsing a list of directories that have a name format
> 'YearWeekNoDay', using the follwoing code
>
>             print list dir[j]
>             print "%s" % (time.strptime (list dir[j], '%Y%U%w'))
>             ttuple = time.strptime (list dir[j], '%Y%U%w')
>             year   = ttuple[0]
>             month  = ttuple[1]
>             day    = ttuple[2]
>             print day, month, year
>
> I get the following output:
>
> 2004123
> (2004, 1, 1, 0, 0, 0, 2, 1, -1)
> 1 1 2004
>
> 2004124
> (2004, 1, 1, 0, 0, 0, 3, 1, -1)
> 1 1 2004
>
> ====
>
> Are you sure you are using the correct format string?
> %U is week number of year [00-53], so I am not sure what happens
> if you combine that with a day of month that surely is not in this week..
>
> Cheers
>  Holger
>

%w (lower case) is day of the week 0 (Sunday) to 6
============
Andy,
you are right, of course. I misread your posting - sorry.
I looked in the source code and this is how I understand it:
Funny as it is, python 2.3.3 strptime simply ignores the %U part in the
format string.
The strptime handling is actually done in lib/_strptime.py, not by the C
strptime function
from time.h any more. Alas, there is no %U handling in there!

You could patch _strptime.py in the following way to reactivate %U
functionality:

$ diff -u -1  _strptime.py.orig _strptime.py
--- _strptime.py.orig   Fri Mar 26 16:44:47 2004
+++ _strptime.py        Fri Mar 26 16:33:18 2004
@@ -434,2 +434,3 @@
     weekday = julian = -1
+    weeknr_set = False
     found_dict = found.groupdict()
@@ -506,3 +507,11 @@
                 tz = 1
-
+        elif group_key == 'U':
+            # if julian is set just ignore the week number
+            if julian == -1:
+                # set the julian number to be in the week with given
number
+                julian = 1 + (int(found_dict['U']) - 1) * 7
+                weeknr_set = True
+                if weekday == -1:
+                    weekday = 0 # set default to 0 (Monday)
+
     # Cannot pre-calculate datetime_date() since can change in Julian
@@ -517,2 +526,10 @@
         datetime_result = datetime_date.fromordinal((julian - 1) +
datetime_date(year, 1, 1).toordinal())
+        if weeknr_set:
+            # correct julian to be the given weekday (which defaults to 0)
+            julian += weekday - datetime_result.weekday()
+            if julian < 1:
+                # ignore negative values, stay in the current year
+                julian = 1
+            datetime_result = datetime_date.fromordinal((julian - 1) +
datetime_date(year, 1, 1).toordinal())
+
         year = datetime_result.year

Note:
Behaviour differs a bit from the results you get with e.g. the python 1..5.2
version.
Since %U expects a 0 for Sunday,..., 6 for Monday, but the week numbering
works differently
(at least in the calendar on my table :
>>>
>>> time.strptime("2004 2 0", "%Y %U %w") # 0 for %U is Sunday
(2004, 1, 11, 0, 0, 0, 6, 11, -1)
>>> time.strptime("2004 2 0", "%Y %U %w") # 0 for %U is Sunday --> Sunday
in week 2, 2004 is Jan. 11
(2004, 1, 11, 0, 0, 0, 6, 11, -1)
>>> time.strptime("2004 2 1", "%Y %U %w") # 1 for %U is Monday --> Monday
in week 2, 2004 is Jan. 5
(2004, 1, 5, 0, 0, 0, 0, 5, -1)
>>>

But this can be easily changed to behave like pre-2.3.3 strptime.

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