[Python-ideas] Optional key to `bisect`'s functions?

[Guido van Rossum]

Bingo. That clinches it. We need to add key=.

On Thu, Feb 9, 2012 at 6:27 AM, Arnaud Delobelle <arnodel at gmail.com> wrote:

> On 9 February 2012 00:25, Guido van Rossum <guido at python.org> wrote:
> > Basically Raymond says "bisect can call the key() function many times,
> which
> > leads to bad design". His alternative, to use a list of (key, value)
> tuples,
> > is often a bit clumsy when passing the sorted list to another function
> (e.g.
> > for printing); having to transform the list using e.g. [v for (k, v) in
> a]
> > feels clumsy and suboptimal.
>
> Also, in Python 3 one can't assume that values will be comparable so
> the (key, value) tuple trick won't work: comparing the tuples may well
> throw a TypeError.  Here's a simple example below.  The class 'Person'
> has no natural order, but we may want to keep a list of people sorted
> by iq:
>
> >>> class Person:
> ...     def __init__(self, height, iq):
> ...         self.height = height
> ...         self.iq = iq
> ...
> >>> arno = Person(184, 101)
> >>> guido = Person(179, 185)
> >>> steve = Person(168, 101)
> >>> key = lambda p: p.iq
> >>> people = []
> >>> bisect.insort(people, (key(arno), arno))
> >>> bisect.insort(people, (key(guido), guido))
> >>> bisect.insort(people, (key(steve), steve))
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> TypeError: unorderable types: Person() < Person()
> >>>
>
> --
> Arnaud
>



-- 
--Guido van Rossum (python.org/~guido)
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