[Tutor] datetime module problem

[Kent Johnson]

Dick Moores wrote:

> from datetime import datetime
> 
> print "Enter 2 dates, first the earlier date, then the later date."
> def getDate():
>     date = raw_input("Enter date as month/day/year, or enter nothing for 
> today: ")
>     if date == "":
>         date = datetime.now()
>         print "Today's date entered"
>     else:
>         date = datetime.strptime(date, '%m/%d/%Y')
>     return date
>    
> print "What's the earlier date?"
> date1 = getDate()
> print
> print "What's the later date?"
> date2 = getDate()
> print
> print "The difference between the dates is", (date2 - date1).days, 'days'
> 
> However, when the earlier date (date1) is today's date entered by just 
> pressing Enter, the result is always 1 day too small. And I don't see 
> how to correct this, other than by adding the 1 (and I'd have to give up 
> using a function, I think). I still don't really get datetime. Help?

It's a rounding error.

In [3]: from datetime import datetime
In [4]: n=datetime.now()
In [5]: n
Out[5]: datetime.datetime(2008, 4, 17, 8, 2, 15, 278631)

Notice n has a time component.

In [8]: y=datetime.strptime('4/18/2008', '%m/%d/%Y')
In [14]: y
Out[14]: datetime.datetime(2008, 4, 18, 0, 0)

y represents midnight on the given date.

In [9]: y-n
Out[9]: datetime.timedelta(0, 57464, 721369)

So y-n is a fractional day, not a whole day.

You could either create n with hours=minutes=0, or round the difference 
up to the next whole number of days.

Kent