gistfile1.py

import datetime
import pytz


def testcase(tzinfo, dt, delta):
    dt = dt.replace(tzinfo=tzinfo)
    earlier = dt - delta
    later = earlier + delta

    assert dt == later
    print "tzinfo      ", tzinfo
    print "dt          ", dt
    print "dst dt      ", tzinfo.dst(dt)
    print "delta       ", delta
    print "earlier     ", earlier
    print "dst earlier ", tzinfo.dst(earlier)
    print "later       ", later
    print "dst later   ", tzinfo.dst(later)
    print


testcase(
    tzinfo=pytz.timezone('US/Eastern'),
    dt=datetime.datetime(2002, 10, 27, 1, 0),
    delta=datetime.timedelta(hours=1))

testcase(
    tzinfo=pytz.timezone('US/Eastern'),
    dt=datetime.datetime(2002, 10, 27, 1, 0),
    delta=-datetime.timedelta(hours=1))

testcase(
    tzinfo=pytz.timezone('US/Eastern'),
    dt=datetime.datetime(2002, 10, 27, 1, 0),
    delta=datetime.timedelta(days=1))

testcase(
    tzinfo=pytz.timezone('US/Eastern'),
    dt=datetime.datetime(2002, 10, 27, 1, 0),
    delta=-datetime.timedelta(days=1))