Question

I use Python to track the version between local SQLite and remote web page. It is useful to compare them by Last-modified and file size information from the HTTP response. I found something interesting during development.

def time_match(web,sql):
  print web,sql
  t1 = time.strptime(web,"%a, %d %b %Y %H:%M:%S %Z")
  t2 = time.strptime(sql,"%Y-%m-%d %H:%M:%S")
  print t1,t2
  if t1==t2:
    print "same time"
  else:
    print "different time"
  return t1==t2

In above code, I tried to decode the time from web and SQLite into internal time and compare them. Let us check out the print screen as following:

Wed, 13 Oct 2010 01:13:26 GMT 2010-10-13 01:13:26
(2010, 10, 13, 1, 13, 26, 2, 286, 0) (2010, 10, 13, 1, 13, 26, 2, 286, -1)
different time

The result shows me that the GMT is correctly decoded, while the default timezone datetime of Python seems as -1. My system timezone is actually +8, Where is the -1 comes from? SQLite?

Answer 1

The -1 at the last position in the time.struct_time object does not mean you are in the ‘UTC-01:00’. It represents the undefined attribute is_dst (since YYYY-MM-DD HH:MM:SS format does not contain any information on the current timezone or daylight saving time mode).

time.strptime('2010-10-15 11:01:02', '%Y-%m-%d %H:%M:%S')
# returns the following on a computer with Central European Sommer Time (CEST, +02:00):
time.struct_time(tm_year=2010, tm_mon=10, tm_mday=15, tm_hour=11, tm_min=1, tm_sec=2, tm_wday=4, tm_yday=288, tm_isdst=-1)