No? Or not necessarily, at least. For example, pytz (a Python timezone library) offers "is_dst" flags for exactly that purpose.

  >>> loc_dt = datetime(2002, 10, 27, 1, 30, 00)
  >>> est_dt = eastern.localize(loc_dt, is_dst=True)
  >>> edt_dt = eastern.localize(loc_dt, is_dst=False)
  >>> print(est_dt.strftime(fmt) + ' / ' + edt_dt.strftime(fmt))
  2002-10-27 01:30:00 EDT-0400 / 2002-10-27 01:30:00 EST-0500

https://pythonhosted.org/pytz/#problems-with-localtime