show_mongo_converts_tzaware_datetimes.py

# A snippet to show that pymongo / mongo converts timezone aware datetime objects to UTC, when saving.

# docker run --env MONGO_INITDB_DATABASE=brain --env MONGO_INITDB_ROOT_USERNAME=root --env MONGO_INITDB_ROOT_PASSWORD=secret --publish-all mongo:4.2
#
# lookup which port it was mapped to:
# $ docker container ls
# CONTAINER ID   IMAGE       COMMAND                  CREATED         STATUS         PORTS                      NAMES
# 8eaf2dd5aedb   mongo:4.2   "docker-entrypoint.s…"   6 minutes ago   Up 6 minutes   0.0.0.0:55000->27017/tcp   brave_moser

import datetime

import pymongo
import pytz

ts = datetime.datetime.fromisoformat("2021-04-19 17:01:50.221").replace(tzinfo=pytz.timezone("UTC"))
btz = pytz.timezone("Europe/Berlin")

c = pymongo.MongoClient("localhost:55000", username="root", password="secret")
c.get_database("db").get_collection("col").drop()

# Insert with "Europe/Berlin"
c.get_database("db").get_collection("col").insert_one({"d": btz.normalize(ts)})
inserted = next(iter(c.get_database("db").get_collection("col").find()))

# Observe inserted is in UTC:
print(f"inserted: {inserted['d']}, utc: {ts}, Berlin: {btz.normalize(ts)}")
# inserted: 2021-04-19 17:01:50.221000, utc: 2021-04-19 17:01:50.221000+00:00, Berlin: 2021-04-19 19:01:50.221000+02:00