Python: UTC vs local timestamp

Question

Why the followings return different timestamp? Is it because datetime.utcnow() doesn't have a timezone? It looks to me that tzinfo=utc is redudant, so I am probably not getting what is utcnow() and how an UTC number could not have a timezone. I guess there is a reason, so please enlight me :)

from datetime import datetime
from pytz import utc

local_seconds = int(datetime.utcnow().timestamp())
utc_seconds = int(datetime.utcnow().replace(tzinfo=utc).timestamp())

My goal is to get the UTC timestamp. It looks like the first method returns the local timestamp (correct me if I am wrong)

EDIT: Where I live the timezone is GMT-5. In fact:

(utc_seconds-local_seconds)/3600 # is equal to -5.0

Answer 1

Following two statements would always return different result.

local_seconds = int(datetime.utcnow().timestamp())
utc_seconds = int(datetime.utcnow().replace(tzinfo=utc).timestamp())

Output:

1585584790
1585604590

You ask why? Because, by the time first statement executes, there is some time spent during execution and now the second statement would fetch you different result because datetime.utcnow() for 2nd statement has changed.

What I assume is, you want to see if both operations would give the same result or not? They definitely would have given the same results :

1. Had you provided them the same input?
2. Had you performed the similar operation from a common library.

To solve 1. change your code like this.

same_time_input = datetime.utcnow()

local_seconds = int(same_time_input.timestamp())
utc_seconds = int(same_time_input.replace(tzinfo=utc).timestamp())

Still the output would not be same, because you are using an external library, and the replace function is not working as you expected.

If you printout the tzinfo from same_time_input, you would see that it doesn't have any timezone info reason of which can be read here. --> Why does datetime.datetime.utcnow() not contain timezone information?

print(same_time_input.tzinfo)

Now, you are trying to give it a timezone info using a separate library which has different implementation internally resulting in slightly off results.