Other notes

Andrew Dalke dalke at dalkescientific.com
Wed Dec 29 08:41:36 CET 2004


Paul Rubin wrote:
> ".." just becomes an operator like + or whatever, which you can define
> in your class definition:
> 
>     class MyClass:
>        def __dotdot__(self, other):
>           return xrange(self.whatsit(), other.whatsit())
> 
> The .. operation is required to return an iterator.

Ahh, I see.

This should be put into a PEP.  Some obvious questions:
  - ".." or "..." ?  The latter is already available for
      use in slices

  - If "..." should the name be "__ellipsis__"?  If ".."
      should the name be "__range___"?

  - Should range(x, y) first attempt x.__range__(y)?

  - Can it be used outside of a for statement?  Ie, does
       x = "a" ... "b"
    return a generic iterator?  Almost certainly as that
    fits in nicely with the existing 'for' syntax.

  - What's the precedence?  Given
      x = a .. b .. c
      x = 1 + 2 .. 5 * 3
      x = 1 ** 5 .. 4 ** 2
     etc., what is meant?  Most likely .. should have the
     lowest precedence, evaluated left to right.

  - is there an "__rdotdot__"?

  - any way to specify "use the normal beginning"?  Like
     for x in .. 5:  # same as 0 .. 5
      -or (the oft rejected)-
     for x in 5:

  - any way to specify "ad infinitum"?  Like
      for x in 0 .. Infinity:
        -or-
      for x in 0 ... :

  - does "for x in 10 .. 0" the same as xrange(10,0) (what
     you propose) or xrange(10, 0, -1)?

  - do strings work for len(s) > 1?  Eg, "A000" .. "A999"?

  - What do you think of (assuming the use of "...")
      for x in 0.....100:?

  - What's the advantage of ".." over, say a function or
    method?  That is, why does the new binary operator
    prove so useful?  In one of my gedanken experiments
    I considered getting the 10th through 20th prime
      for x in primes(10) .. primes(20):
    but that seems clumsier than
      for x in primes_between(10, 20):
    in part because it requires "primes(10)" to have some
    meaning.  I suppose
      for x in primes(10) .. 20:
    could also work though that should in my mind generate
    primes up to the number 20 and not the 20th prime.
    Note that primes(10) cannot return the 10th prime as
    the value 29.

				Andrew
				dalke at dalkescientific.com




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