Timezones how the fuck do they work

tztest.py

from datetime import datetime, tzinfo, timedelta

class TimeZone(tzinfo):
  def __init__(self, name, offset):
    self.name = name
    self.offset = offset
    self.timedelta = timedelta(hours=offset)

  def utcoffset(self, dt):
    return self.timedelta

  def dst(self, dt):
    return self.timedelta

  def tzname(self, dt):
    return self.name

bst = TimeZone('BST', 1)
gmt = TimeZone('UTC', 0)

datetime_in_bst = datetime.now(bst)
datetime_in_gmt = datetime.now(gmt)
now_without_tz = datetime.now()

print datetime_in_bst.strftime("%H:%M:%S %Z")
print datetime_in_gmt.strftime("%H:%M:%S %Z")

print datetime_in_gmt.astimezone(bst).strftime("%H:%M:%S %Z")

print now_without_tz.strftime("%H:%M:%S %Z")
try:
  print now_without_tz.astimezone(bst).strftime("%H:%M:%S %Z")
except Exception, e:
  print e.message

now_with_tz = now_without_tz.replace(tzinfo=gmt)
print now_with_tz.astimezone(bst).strftime("%H:%M:%S %Z")