Python3.9でdatetimeの扱い方法のチートシート的メモ書き
from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

### 生成 ###

## 現在時刻
zone = ZoneInfo("Asia/Tokyo")
now = datetime.now(zone)
print(f'現在時刻: {now}')

# >>>>>>>>>>>>>>>>>
# 現在時刻: 2021-04-07 11:34:20.971192+09:00
# >>>>>>>>>>>>>>>>>

## 指定時刻
first_day_2021 = datetime(2021, 1, 1, 0, 0, 0, tzinfo=zone)
print(f'指定時刻: {first_day_2021}')

# >>>>>>>>>>>>>>>>>
# 指定時刻: 2021-01-01 00:00:00+09:00
# >>>>>>>>>>>>>>>>>

## unixtimestampからの生成
from_unixtimestamp = datetime.fromtimestamp(0, tz=zone)
print(f'unixtimestampから: {from_unixtimestamp}')

# >>>>>>>>>>>>>>>>>
# unixtimestampから: 1970-01-01 09:00:00+09:00
# >>>>>>>>>>>>>>>>>

### 演算 ###

## 10秒足す
add_10sec = first_day_2021 + timedelta(seconds=10)
print(f'10秒足す: {add_10sec}')

# >>>>>>>>>>>>>>>>>
# 10秒足す: 2021-01-01 00:00:10+09:00
# >>>>>>>>>>>>>>>>>

## 10分引く
minus_10mins = first_day_2021 - timedelta(minutes=10)
print(f'10分引く: {minus_10mins}')

# >>>>>>>>>>>>>>>>>
# 10分引く: 2020-12-31 23:50:00+09:00
# >>>>>>>>>>>>>>>>>

## 1時間足す
add_1hour = first_day_2021 + timedelta(hours=1)
print(f'1時間足す: {add_1hour}')

# >>>>>>>>>>>>>>>>>
# 1時間足す: 2021-01-01 01:00:00+09:00
# >>>>>>>>>>>>>>>>>

## 1日引く
minus_1day = first_day_2021 - timedelta(days=1)
print(f'1日引く: {minus_1day}')

# >>>>>>>>>>>>>>>>>
# 1日引く: 2020-12-31 00:00:00+09:00
# >>>>>>>>>>>>>>>>>

### 文字列出力 ###

## 2021-01-01 00:00:00
print(now.strftime("%Y-%m-%d %H:%M:%S"))

# >>>>>>>>>>>>>>>>>
# 2021-04-07 11:34:20
# >>>>>>>>>>>>>>>>>


## 2021/01/01 00:00:00
now.strftime("%Y/%m/%d %H:%M:%S")
print(now.strftime("%Y/%m/%d %H:%M:%S"))

# >>>>>>>>>>>>>>>>>
# 2021/04/07 11:34:20
# >>>>>>>>>>>>>>>>>
参考
