[Python-ideas] 'default' keyword argument for max(), min()

[George Sakkis]

On Thu, Apr 16, 2009 at 7:07 PM, Raymond Hettinger <python at rcn.com> wrote:

> I think you're focusing on just one solution, one that involves piling-up
> too many extensions in one function that should be dirt simple.  There
> are many other approaches:  try/except, wrap the input in a default
> itertool, use all(), use next(it, default) to test the first value, etc.

Right, I've now grown used to wrapping it in try/except in advance
just to be on the safe side; in the past I had to go back and fix it
after it has already bombed with a ValueError once. So yes, overall I
find the proposed parameter a handy convenience, not a fix to a
glaring omission.

I think what it boils down to is how exceptional is the empty iterable
for the overall task at hand. Does what follows the min/max
computation differ substantially when the input is empty from when
it's not, or does the following code can remain blissfully ignorant
about how was the value determined ? In the former case, raising an
exception is a feature since it forces the user to think about this
case and handle it explicitly. If not, then it's just extra
boilerplate we could do without.

A good example of the first case is division by zero: typically the
course of action is totally different if some intermediate computation
involves division by zero; you can't just replace it with some default
and continue with the rest computations as if nothing happened
(although a default might make sense as the "final" result, depending
on the application). OTOH, code that uses dict.get() or getattr() with
a default doesn't really care whether the key/attribute is actually in
the queried dict/object, the following logic remains the same.

So the bottom line is, are most use cases of taking the min/max of an
empty iterable closer to these that involve an intermediate
DivisionByZero or to those that involve a missing key/attribute ? I
don't have a general answer, both make sense under different
circumstances.

George


PS: Thanks for the default() recipe, seems generally useful, not only
for min/max.