default-arg-anti-pattern.py

>>> from datetime import datetime
>>> def today(dt=datetime.now()):
...     print(dt)
...
>>> today()
2020-12-12 22:18:26.432268
# oops
>>> today()
2020-12-12 22:18:26.432268
>>> today()
2020-12-12 22:18:26.432268
>>> from datetime import datetime
>>> def today(dt=None):
...     if dt is None:
...         dt = datetime.now()
...     print(dt)
...
>>> today()
2020-12-12 22:19:11.617223
# better
>>> today()
2020-12-12 22:19:12.545453
>>> today()
2020-12-12 22:19:14.145179