Is that possible to "recover" UTC time given local time and geometrical time shift?

I now have server local time and a hour shift to UTC(say +5, -8, etc), how can I recover it to UTC?

Note that it's not as intuitive as it is because of summer time. Currently I am in EDT, which should be UTC+5, but in fact, in summer, we only +4. And unfortunately I don't (want to) know the timezone of the server so I am not sure whether it's possible to calculate the UTC with given info.

My target language is python, but if an solution exists, the language itself shouldn't be a big problem.

Why I have such restriction, is because of this. It just doesn't return a good text timezone description instead of a number.

following is a real element in practice from my server:

<RegionalSettings>
  <Language>1033</Language>
  <Locale>1033</Locale>
  <AdvanceHijri>0</AdvanceHijri>
  <CalendarType>1</CalendarType>
  <Time24>False</Time24>
  <TimeZone>300</TimeZone>
  <SortOrder>2070</SortOrder>
  <Presence>True</Presence>
</RegionalSettings>

notice here the timezone field

<TimeZone>300</TimeZone>

it's in minutes, so it tells me I am somewhere in UTC+5, but not a honest timeshift to UTC.

via Chebli Mohamed