[Python-Dev] Re: PEP 326: A Case for All

[Phillip J. Eby]

At 12:00 PM 1/4/04 -0800, Josiah Carlson wrote:
>Further uses of All will be left as an exercise to whomever wants to use
>it.

Um, then why don't those people just write their own 'All'?  It's not like 
they all need to be using the same definition of 'All', so why put it in 
Python?

The "Motivation" section of PEP 326 does not answer this 
question.  Although it claims "hundreds of algorithms", it demonstrates 
only *one*: finding the minimum of a sequence.

The example shows three versions of finding a minimum of a sequence, to 
show that it's easier with 'All'.  But that's a straw man argument: the 
*easiest* way to get the desired behavior is just to use 'min(seq)' and not 
write any new functions at all!

So, essentially, the "Motivation" section might as well not be in the PEP, 
because it provides no actual motivation at all.  You need to find a better 
algorithm to cover.

And don't bother using "find the pair x,y from a sequence of pairs where 
'x' is the lowest item" as a substitute, because again the answer is 
'min(seq)'.  And even if you say, "yes but we don't want 'y' to be 
compared", there's always:

def min_key(pairs):
     minX, chosenY = pairs[0]
     for x,y in pairs[1:]
         if x<minX:
             minX, chosenY = x,y
     return minX, chosenY

or, if you prefer using iterators to slicing:

def min_key(pairs):
     pairs = iter(pairs)
     minX, chosenY = pairs.next()
     for x,y in pairs
         if x<minX:
             minX, chosenY = x,y
     return minX, chosenY

So, please pick some examples that aren't based on finding minimums, and 
that also illustrate why it's important that Python itself include this 
concept.  Can you show why it's a bad thing for people to implement their 
own infinity-like type(s)?  In what areas does the standard library show a 
need for such an object?  And so on.

Without more motivation for the proposal, you're likely to see continued 
opposition to the PEP.