Arithmetic sequences in Python

[Antoon Pardon]

Op 2006-01-16, Alex Martelli schreef <aleax at mail.comcast.net>:
> Paul Rubin <http://phr.cx@NOSPAM.invalid> wrote:
>
>> Steven D'Aprano <steve at REMOVETHIScyber.com.au> writes:
>> > For finite sequences, your proposal adds nothing new to existing
>> > solutions like range and xrange.
>> 
>> Oh come on, [5,4,..0] is much easier to read than range(5,-1,-1).
>
> But not easier than reversed(range(6)) [[the 5 in one of the two
> expressions in your sentence has to be an offbyone;-)]]

Why don't we give slices more functionality and use them.
These are a number of ideas I had. (These are python3k ideas)

1) Make slices iterables. (No more need for (x)range)

2) Use a bottom and stop variable as default for the start and
   stop attribute. top would be a value that is greater than
   any other value, bottom would be a value smaller than any
   other value.

3) Allow slice notation to be used anywhere a value can be
   used.

4) Provide a number of extra operators on slices.
   __neg__ (reverses the slice)
   __and__ gives the intersection of two slices
   __or__ gives the union of two slices

5) Provide sequences with a range (or slice) method.
   This would provide an iterator that iterates over
   the indexes of the sequences. A slice could be
   provided


  for i in xrange(6):

would then become

  for i in (0:6):

for a reversed sequence

  for i in reversed(xrange(6)):

would become

  for i in - (0:6):


  for i, el in enumerate(sequence):

would become

  for i in sequence.range():
    el = sequence[i]

But the advantage is that this would still work when
someone subclasses a list so that it start index
is an other number but 0.

If you only wanted every other index one could do
the following

  for i in sequence.range(::2):

which would be equivallent to

  for i in sequence.range() & (::2):

-- 
Antoon Pardon