Python dateutil.parser throws "ValueError: day is out of range for month"

Question

I have a the following code that runs fine with input format like {Year}/{Month} except when it comes to 1994/02

Here is the sample code

>>> import dateutil.parser as dtp
>>> dtp.parse('1994/01')
datetime.datetime(1994, 1, 29, 0, 0)
>>> dtp.parse('1994/03')
datetime.datetime(1994, 3, 29, 0, 0)
>>> dtp.parse('1994/02')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/antony/.virtualenvs/comp-invest/lib/python2.7/site-packages/dateutil/parser.py", line 720, in parse
    return DEFAULTPARSER.parse(timestr, **kwargs)
  File "/Users/antony/.virtualenvs/comp-invest/lib/python2.7/site-packages/dateutil/parser.py", line 317, in parse
    ret = default.replace(**repl)
ValueError: day is out of range for month

As you can see, the code works fine with 1994/01 and 1994/03, but fails with 1994/02 Does this have anything to do with leap year? But more important, how do I get around this problem and make my code work again?

Thanks

Lendlease

It looks like it is defaulting to 29 (today's day) for the day and there isn't normally 29 days in February. Not sure if February 1994 was a leap year. – Delia

For the record, 1994 was not (1992 and 1996 were). – Winder

Ran into the same thing. One of my favorite "features" in a long time. Code that only breaks at the end of a month... – Floc

Answer 1

dtp.parse is filling in the missing day with the current date's day. You ran the code on 2013/01/29 and day 29 does not exist in February (i.e. 1994/02/29).

Use this instead:

dtp.parse('1994/01'+'/01')

It will give consistent results (first day of month) regardless of when the code is executed.

Facilitate

you can derive that from the returned value by the way datetime.datetime(1994, 1, 29, 0, 0). – Facilitate

Thanks! I must be tired..so I didn't connect the dots. In fact, the code did not run into issues until today...so I was rather puzzled about that, but you are a genius at pointing out the real cause. Thanks! SO doesn't let me mark you as answer until 7 min later..so give it another 7 or so, and I will mark this as answered. Thanks! – Lendlease

Answer 2

This was a bug in dateutil that has since been fixed. Version 2.5.0 and higher will no longer have this issue.

If you must use an earlier version, I think that the "correct" way to handle things is to specify the default parameter:

from dateutil.parser import parse
from datetime import datetime, date

# First of the current month, at midnight.
default_date = datetime.combine(date.today(), datetime.min.time()).replace(day=1)
dt = parse('1994/01', default=default_date)

This will default to the 1st of the month rather than the current day.

Sake