Question

What is happening here?

This expected:

>>> datetime.min - timedelta(days=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: date value out of range

Unexpected:

>>> datetime.min - timedelta(days=2)
datetime.datetime(1, 0, 255, 0, 0)

>>> datetime.min > (datetime.min - timedelta(days=2))
True

In python, what do these values mean when you subtract from datetime.min? What dates do they represent? Why do some cases not trigger an OverflowError?

Answer 1

Because you need to upgrade to Python 2.6 or later, which fixed this bug.

$ python2.5 -c 'import datetime; print(datetime.datetime.min - datetime.timedelta(days=2))'
0001-00-255 00:00:00
$ python2.6 -c 'import datetime; print(datetime.datetime.min - datetime.timedelta(days=2))'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OverflowError: date value out of range
$ python2.7 -c 'import datetime; print(datetime.datetime.min - datetime.timedelta(days=2))'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OverflowError: date value out of range
$ python3.3 -c 'import datetime; print(datetime.datetime.min - datetime.timedelta(days=2))'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OverflowError: date value out of range

Do you need someone to track down the bug number, patch, and python-dev discussion, or is that enough information for you?