How to convert local time string to UTC?

Question

How do I convert a datetime string in local time to a string in UTC time?

I\'m sure I\'ve done this before, but can\'t find it and SO will hopefull

Answer 1

Here's a summary of common Python time conversions.

Some methods drop fractions of seconds, and are marked with (s). An explicit formula such as ts = (d - epoch) / unit can be used instead (thanks jfs).

• struct_time (UTC) → POSIX (s):
  calendar.timegm(struct_time)
• Naïve datetime (local) → POSIX (s):
  calendar.timegm(stz.localize(dt, is_dst=None).utctimetuple())
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → POSIX (s):
  calendar.timegm(dt.utctimetuple())
• Aware datetime → POSIX (s):
  calendar.timegm(dt.utctimetuple())
• POSIX → struct_time (UTC, s):
  time.gmtime(t)
  (see comment from jfs)
• Naïve datetime (local) → struct_time (UTC, s):
  stz.localize(dt, is_dst=None).utctimetuple()
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → struct_time (UTC, s):
  dt.utctimetuple()
• Aware datetime → struct_time (UTC, s):
  dt.utctimetuple()
• POSIX → Naïve datetime (local):
  datetime.fromtimestamp(t, None)
  (may fail in certain conditions, see comment from jfs below)
• struct_time (UTC) → Naïve datetime (local, s):
  datetime.datetime(struct_time[:6], tzinfo=UTC).astimezone(tz).replace(tzinfo=None)
  (can't represent leap seconds, see comment from jfs)
• Naïve datetime (UTC) → Naïve datetime (local):
  dt.replace(tzinfo=UTC).astimezone(tz).replace(tzinfo=None)
• Aware datetime → Naïve datetime (local):
  dt.astimezone(tz).replace(tzinfo=None)
• POSIX → Naïve datetime (UTC):
  datetime.utcfromtimestamp(t)
• struct_time (UTC) → Naïve datetime (UTC, s):
  datetime.datetime(*struct_time[:6])
  (can't represent leap seconds, see comment from jfs)
• Naïve datetime (local) → Naïve datetime (UTC):
  stz.localize(dt, is_dst=None).astimezone(UTC).replace(tzinfo=None)
  (exception during DST transitions, see comment from jfs)
• Aware datetime → Naïve datetime (UTC):
  dt.astimezone(UTC).replace(tzinfo=None)
• POSIX → Aware datetime:
  datetime.fromtimestamp(t, tz)
  (may fail for non-pytz timezones)
• struct_time (UTC) → Aware datetime (s):
  datetime.datetime(struct_time[:6], tzinfo=UTC).astimezone(tz)
  (can't represent leap seconds, see comment from jfs)
• Naïve datetime (local) → Aware datetime:
  stz.localize(dt, is_dst=None)
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → Aware datetime:
  dt.replace(tzinfo=UTC)

Source: taaviburns.ca