That can work for you:

Convert UTC datetime string to local datetime

I copied the code to make it easier to tackle, I indicate it's another person's answer anyway.

from datetime import datetime,tzinfo,timedelta

class Zone(tzinfo):
    def __init__(self,offset,isdst,name):
        self.offset = offset
        self.isdst = isdst
        self.name = name
    def utcoffset(self, dt):
        return timedelta(hours=self.offset) + self.dst(dt)
    def dst(self, dt):
            return timedelta(hours=1) if self.isdst else timedelta(0)
    def tzname(self,dt):
         return self.name

GMT = Zone(0,False,'GMT')
EST = Zone(-5,False,'EST')

print(datetime.utcnow().strftime('%m/%d/%Y %H:%M:%S %Z'))
print(datetime.now(GMT).strftime('%m/%d/%Y %H:%M:%S %Z'))
print(datetime.now(EST).strftime('%m/%d/%Y %H:%M:%S %Z'))

t = datetime.strptime('2011-01-21 02:37:21','%Y-%m-%d %H:%M:%S')
t = t.replace(tzinfo=GMT)
print(t)
print(t.astimezone(EST))

I've tried it in my Python Notebook and works perfectly.

ISO 8601 allows a compact representation with no separators except for the T, so I like to use this one-liner to get a quick timestamp string:

>>> datetime.datetime.now(datetime.UTC).strftime("%Y%m%dT%H%M%S.%fZ")
'20180905T140903.591680Z'

If you don't need the microseconds, just leave out the .%f part:

>>> datetime.datetime.now(datetime.UTC).strftime("%Y%m%dT%H%M%SZ")
'20180905T140903Z'

For local time:

>>> datetime.datetime.now(datetime.timezone(datetime.timedelta(hours=-5))).strftime("%Y-%m-%dT%H:%M:%S%:z")
'2018-09-05T14:09:03-05:00'

In general, I recommend you leave the punctuation in. RFC 3339 recommends that style because if everyone uses punctuation, there isn't a risk of things like multiple ISO 8601 strings being sorted in groups on their punctuation. So the one liner for a compliant string would be:

>>> datetime.datetime.now(datetime.UTC).strftime("%Y-%m-%dT%H:%M:%SZ")
'2018-09-05T14:09:03Z'

iso = time.strftime('%Y-%m-%dT%H:%M:%SZ', timetup)

The last format charater ‘Z’ is not necessary, such as

iso = time.strftime('%Y-%m-%dT%H:%M:%S', timetup)

You will get time string like '2015-11-05 02:09:57'