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Python what is the correct timefomat for: 2018-11-13T20:20:39+00:00

I need to get a now() timestamp like this following: 2018-11-13T20:20:39+00:00 What is the correct format string for this?

To get an isoformat() string with time zone offset (the +00:00 at the end of the string) you need to supply a tzinfo object when constructing the datetime. the easiest way to do this is with the pytz library - pytz.timezone("UTC") returns the tzinfo for UTC.
There's another issue though, which is that technically that string doesn't quite match default isoformat() output because it has no microseconds. So a full example for the output requested would be:
import datetime
import pytz
datetime.datetime.now(tz=pytz.timezone("UTC")).replace(microsecond=0).isoformat()

This appears to be the isoformat.
You could use
import datetime as dt
# Get current time in utc
# Because the datetime object is timezone aware the +00:00 will be printed
current_time = dt.datetime.now(dt.timezone.utc)
# timespec will round the solution upto seconds
iso_string = current_time.isoformat(timespec="seconds")
print(iso_string)
will print 2019-11-19T19:51:46+00:00.

Timestamp to non UTC Datetime object is substracting hours twice

I have the following timestamp 1550588656 which translates to 2019-02-19 15:04:16+00:00 in UTC time convention.
I want to convert it to my country's time convention (UTC or GMT -3 in this time of the year) so it should translate to 2019-02-19 12:04:16+00:00
I have read on other SO questions that first I have to convert the timestamp to an UTC aware Datetime object and then localize it, I'm doing it like this
# string format time
naive_datetime = datetime.fromtimestamp(timestamp).strftime('%Y-%m-%d %H:%M:%S')
# string parse time
naive_datetime = datetime.strptime(naive_datetime, "%Y-%m-%d %H:%M:%S")
# make naive Datetime object UTC aware
utc_datetime = naive_datetime.replace(tzinfo=pytz.UTC)
So now it's not a naive Datetime object, from here I should be able to localize it to my country's timezone. In Python that is pytz.timezone('America/Santiago')
So it should go something like this
cltime = pytz.timezone('America/Santiago')
local_datetime = utc_datetime.astimezone(cltime)
But I'm getting 2019-02-19 09:04:16-03:00 (UTC or GTM -6 ) as a result and I don't know why.
Can someone explain? My intuition tells me it's probably a simple thing I'm not looking at, but I've spent some minutes in it and I haven't been able to tell yet.

If you look at the documentation for fromtimestamp:
Return the local date and time corresponding to the POSIX timestamp
So the problem is that it is already doing a conversion from UTC to the local time, and you're doing it a second time.

First of all you have epoc time (UTC timestamp). You need to convert it into datetime object (native) which is followed by converting native time to aware time and than finally convert it to your local time.
Convert your timestamp to native datetime object
native_datetime = datetime.fromtimestamp(1550588656)
convert native datetime object to aware time (add timezone info, will add timezone info to native timezone UTC for current)
import pytz
utc_time = native_datetime.replace(tzinfo=pytz.timezone("UTC"))
localising aware datetime to your local datetime
local_time = utc_time.astimezone(pytz.timezone("America/Santiago"))
You can replace "America/Santiago" with your local time zone
I think this would help you to solve your problem. Thanks!

Python Datetime object

I am currently having an issue converting an incoming datetime string to a datetime object using Python's built in strptime() method. Here is what I currently have:
def fixDateTimeField(datetimeString):
# Convert from 2012-08-07T00:00:00Z to 2012-08-07T00:00:00.000Z
datetime_object = datetime.strptime(datetimeString, "%y-%m-%dT%H:%M:%SZ")
return datetime_object
Like the comment says, I am trying to convert the string "2012-08-07T00:00:00Z" to a datetime object that looks like 2012-08-07T00:00:00.000Z but I am getting an error in my console that says: "ValueError: time data '2012-08-07T00:00:00Z' does not match format '%y-%m-%dT%H:%M:%SZ'". The format seems correct to me and i'm not seeing the issue.
Thanks in advance!

%y is for two-digit years. You have a four-digit year.
Try using %Y instead.
>>> from datetime import datetime
>>> datetimeString = "2012-08-07T00:00:00Z"
>>> print(datetime.strptime(datetimeString, "%Y-%m-%dT%H:%M:%SZ"))
2012-08-07 00:00:00

A nice way to parse your iso-8601 datetime string "2012-08-07T00:00:00Z" to a datetime object is using dateutil.
import dateutil.parser
yourdate = dateutil.parser.parse(datestring)
With strptime:
datetime.datetime.strptime( "2007-03-04T21:08:12", "%Y-%m-%dT%H:%M:%S")
Works. As an other answer said, the Y must be capitalized for strptime to work with 4 digit years.

Convert an arbitrary date time in one time zone and convert it to another timezone by using python

I need to convert an arbitrary datetime string for example "2015-10-01 12:20:00 UTC" and convert it to another timezone for example "Europe/Istanbul" with using a simple code in python
I read these answers/questions:
Python Timezone conversion
Python - Convert UTC datetime string to local datetime
but they are not clear and all of them convert nowtime but I need convert any time in any timezone to another arbitrary zonetime

You can do it easily with modules datetime and dateutil:
from datetime import datetime
from dateutil import tz
dobj = datetime.strptime("2015-10-01 12:20:00", '%Y-%m-%d %H:%M:%S')
dobj = dobj.replace(tzinfo=tz.gettz("UTC"))
print(dobj)
print(dobj.astimezone(tz.gettz("Europe/Istanbul")))
Output:
$ python2.7 time.py
2015-10-01 12:20:00+00:00
2015-10-01 15:20:00+03:00

Local Time To UTC time pytz

I converted python datetime with help of pytz.
Convertion is like this
2013-08-23T09:53:03 to 2013-08-23T15:23:03+05:30 (time is changed
according timezone)
now the problem is "At at another loaction i get time as string 2013-08-23T15:23:03+05:30 how can i convert this string to 2013-08-23T09:53:03
thanks in advance

You can use the very useful dateutil package
from dateutil import parser
import pytz
UTC = pytz.timezone('UTC')
date = parser.parse("2013-08-23T15:23:03+05:30")
dateutc = date.astimezone(UTC)
print dateutc.isoformat()
# or user strptime to have in the format you want (without time zone)
print dateutc.strftime("%Y-%m-%dT%H:%M:%S")