[Python-ideas] Have max and min functions ignore None

[Terry Reedy]

On 12/28/2015 11:08 PM, Franklin? Lee wrote:
> What do people think about having `max` and `min` ignore `None`?
>
> Examples:
>      max(1, None) == 1
>      min(1, None) == 1

This amounts to saying that the comparisions 1 < None and 1 > None are 
both defined and both True.

>      max([1, None]) == 1
>      max(None, None) == max() or max(None, None) == max([])
>
> (The last one currently throws two different errors.)
>
>
> This change would allow one to use `None` as a default value. For example,
>
>      def my_max(lst):
>          best = None
>
>          for x in lst:
>              best = max(best, x)
>
>          return best

rewrite this as

def my_best(iterable):
     it = iter(iterable)
     try:
         best = it.next()
     except StopIteration:
         raise ValueError('Empty iterable has no maximum')
     for x in it:
         if x > best:
             best = x


> Currently, you would initialize `best` to the first element,

Since an empty iterable has no max (unless one wants to define the 
equivalent of float('-inf') as a default), initializing with the first 
element is the proper thing to do.

...

> I'm concerned about this silencing some bugs which would have been
> caught before. I'm also worried about whether it would make sense to
> people learning Python.

None currently means 'no value', which means that most operations on 
None are senseless.

-- 
Terry Jan Reedy