[Numpy-discussion] Release of 1.0b5 this weekend

Charles R Harris charlesr.harris at gmail.com
Tue Aug 29 18:17:36 CDT 2006


On 8/29/06, Charles R Harris <charlesr.harris at gmail.com> wrote:
>
> On 8/29/06, Tim Hochberg <tim.hochberg at ieee.org> wrote:
>
> > David M. Cooke wrote:
> > > On Tue, 29 Aug 2006 14:03:39 -0700
> > > Tim Hochberg <tim.hochberg at ieee.org> wrote:
> > >
> > >
> > >> Of these,  clip, conjugate and round support an 'out' argument like
> > that
> > >> supported by ufunces;  byteswap has a boolean argument telling it
> > >> whether to perform operations in place; and sort always operates in
> > >> place. Noting that the ufunc-like methods (max, argmax, etc) appear
> > to
> > >> support the 'out' argument as well although it's not documented for
> > most
> > >> of them, it looks to me as if the two odd methods are byteswap and
> > sort.
> > >> The method situation could be made more consistent by swapping the
> > >> boolean inplace flag in byteswapped with another 'out' argument and
> > also
> > >> having sort not operate in place by default, but also supply an out
> > >> argument there. Thus:
> > >>
> > >> b = a.sort()   # Returns a copy
> > >> a.sort(out=a) # Sorts a in place
> > >> a.sort(out=c) # Sorts a into c (probably just equivalent to c =
> > a.sort()
> > >> in this case since we don't want to rewrite the sort routines)
> > >>
> > >
> > > Ugh. That's completely different semantics from sort() on lists, so I
> > think
> > > it would be a source of bugs (at least, it would mean keeping two
> > different
> > > ideas of .sort() in my head).
> > >
> > Thinking about it a bit more, I'd leave sort alone (returning None and
> > all).. I was (over)reacting to changing to sort to return self, which
> > makes the set of methods both less consistent within itself, less
> > consistent with python and more error prone IMO, which seems the worst
> > possibility.
>
>
> Here is Guido on sort:
>
> I'd like to explain once more why I'm so adamant that *
> sort*() shouldn't
> *return* 'self'.
>
> This comes from a coding style (popular in various other languages, I
> believe especially Lisp revels in it) where a series of side effects
>
> on a single object can be chained like this:
>
>   x.compress().chop(y).*sort*(z)
>
> which would be the same as
>
>   x.compress()
>   x.chop
> (y)
>   x.*sort*(z)
>
> I find the chaining form a threat to readability; it requires that the
> reader must be intimately familiar with each of the methods.  The
>
> second form makes it clear that each of these calls acts on the same
> object, and so even if you don't know the class and its methods very
> well, you can understand that the second and third call are applied to
>
> x (and that all calls are made for their side-effects), and not to
> something else.
>
> I'd like to reserve chaining for operations that *return* new values,
>
> like string processing operations:
>
>   y = x.rstrip("\n").split(":").lower()
>
> There are a few standard library modules that encourage chaining of
> side-effect calls (pstat comes to mind).  There shouldn't be any new
>
> ones; pstat slipped through my filter when it was weak.
>
> So it seems you are correct in light of the Python philosophy. For those
> operators that allow specification of out I would still like to see a
> special value that means inplace, I think it would make the code clearer. Of
> course, merely having the out flag violates Guido's intent. The idea seems
> to be that we want some way to avoid allocating new memory. So maybe
> byteswap should be inplace and return None, while a copyto method could be
> added. Then one would do
>
> a.copyto(b)
> b.byteswap()
>
> instead of
>
> b = a.byteswap()
>
>

To expand on this a bit. Guidos philosophy, combined with a desire for
memory efficiency, means that methods like byteswap and clip, which use the
same memory, should operate inplace and return None. Thus, instead of

b = a.clip(...)

use

b = a.copy()
b.clip(...)

Hey, it's a risc machine. If we did this, then functions could always return
copies:

b = clip(a,...)

Chuck
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