Weird arithmetic with datetimes and relativedelta

Question

Is it safe to multiply relativedelta objects? I'm seeing some weird and inconsistent behaviour, and can't find it documented what sorts of arithmetic are supported by this class (if any)

>>> from datetime import datetime
>>> from dateutil.relativedelta import relativedelta
>>> datetime.now() + relativedelta(days=2)
datetime.datetime(2014, 5, 30, 12, 24, 59, 173941)
>>> datetime.now() + relativedelta(days=1) * 2
# TypeError: integer argument expected, got float

On the other hand:

>>> relativedelta(days=2) == relativedelta(days=1) * 2
True

Full traceback (with python 2.7.5 and dateutil 1.5):

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/dateutil/relativedelta.py", line 261, in __radd__
    day = min(calendar.monthrange(year, month)[1],
  File "/usr/lib/python2.7/calendar.py", line 121, in monthrange
    day1 = weekday(year, month, 1)
  File "/usr/lib/python2.7/calendar.py", line 113, in weekday
    return datetime.date(year, month, day).weekday()
TypeError: integer argument expected, got float

Answer 1

You've run into a known bug in relativedelta's handling of multiplication, since fixed. It only affects Python 2.7 or newer (call signatures of certain functions were tightened).

Upgrade your python-dateutils package to version 2.1 or newer.

Don't be put off by the 2.0-is-Python-3-only misinformation on the project documentation; 2.1 and 2.2 are Python 2 and 3 cross-compatible.