Exceptions

What is the best way of dealing with invalid argument?
Throw an exception or return null?

Lets have an example. I was writing this function that
creates date objects for dates in between 2000-01-01 and
2999-12-31

Looks like this:
<code>
def createDate(date):
    try:
        y, m, d = date
        if(y < 0): return None
        if(y < 2000): y += 2000
        if(y > 2999): return None
        return datetime.date(y, m, d)
    except ValueError:
        return None
</code>

What should i do here? Should i just let the ValueError
error propagate up the stack, maybe throw my own ValueError exceptions in stead of returning None or should i
invent my own exception and throw that instead of ValueError,
or just leave it as it is?


What would you do?

>in b4 "dat shitty language"

>>3
The problem with that is that i can no longer distinguish between my own errors and errors due to the fact that i suck.