Fix for datetime conversion to integer and back to string; was 1 hour off

[La Uruguaya]

I searched this group for a solution to a problem I had converting
dates from a string format to integer (in seconds since 1970) and back
to strings.  During some times of the year, the conversion didn't do
a perfect round trip and I ended up with a datetime that differed from
the original datetime by one hour.  I found 2 postings with variations
on the problem, but not a solution.  I implemented the following
solution and wanted to share it in case somebody needs it later.


import time

DATE_FORMAT = "%Y/%m/%d %H:%M:%S"

def date2int(strdate):
    result = 0
    try:
       tuple = time.strptime(strdate, DATE_FORMAT)
       result = time.mktime(time.strptime(strdate, DATE_FORMAT))
    except:
       pass
    return (result, tuple)

def correctForDaytime(tup):
    lst = list(tup)
    lst[3] -= tup[-1] # if this is zero, then this is a no op
    lst[-1] = 0
    return tuple(lst)

def int2date(intdate):
    result = ''
    if intdate > 0:
       try:
          tuple = time.localtime(intdate)
          tuple = correctForDaytime(tuple) # commenting this line out
will show you the bug
          result = time.strftime(DATE_FORMAT, tuple)
       except:
          pass
    return (result, tuple)

def f(t1str):
    (t1int, tup1) = date2int(t1str)
    (t1str2, tup2) = int2date(t1int)
    print t1str, "->", t1int
    print t1int, "->", t1str2
    if tup1 == tup2:
       print "SAME", tup1, tup2
    else:
       print "DIFF", tup1, tup2
    if t1str != t1str2:
       print "FAILED", t1str, t1str2 
    else:
       print "OK"

f("2003/01/15 11:15:00")
f("2003/02/15 11:15:00")
f("2003/03/15 11:15:00")
f("2003/04/15 11:15:00")
f("2003/05/15 11:15:00")
f("2003/06/15 11:15:00")
f("2003/07/15 11:15:00")
f("2003/08/15 11:15:00")
f("2003/09/15 11:15:00")
f("2003/10/15 11:15:00")
f("2003/11/15 11:15:00")
f("2003/12/15 11:15:00")

f("2003/01/03 11:15:00")
f("2003/02/03 11:15:00")
f("2003/03/03 11:15:00")
f("2003/04/03 11:15:00")
f("2003/05/03 11:15:00")
f("2003/06/03 11:15:00")
f("2003/07/03 11:15:00")
f("2003/08/03 11:15:00")
f("2003/09/03 11:15:00")
f("2003/10/03 11:15:00")
f("2003/11/03 11:15:00")
f("2003/12/03 11:15:00")

f("2003/01/27 11:15:00")
f("2003/02/27 11:15:00")
f("2003/03/27 11:15:00")
f("2003/04/27 11:15:00")
f("2003/05/27 11:15:00")
f("2003/06/27 11:15:00")
f("2003/07/27 11:15:00")
f("2003/08/27 11:15:00")
f("2003/09/27 11:15:00")
f("2003/10/27 11:15:00")
f("2003/11/27 11:15:00")
f("2003/12/27 11:15:00")