[Python-Dev] PEP 289: Generator Expressions (second draft)

[Greg Ewing]

Guido:

> > I probably missed it in this monster of a thread, but how do
> > generator expressions do this?  It seems that they'd only make
> > reduce more efficient, but it would still be just as needed as
> > before.
> 
> All we need is more standard accumulator functions like sum().  There
> are many useful accumulator functions that aren't easily expressed as
> a binary operator but are easily done with an explicit iterator
> argument, so I am hopeful that the need for reduce will disappear.

But this would still be true even if we introduced such functions
*without* generator expressions, i.e.  given some new standard
accumulator foo_accumulator which accumulates using foo_function, you
can write

  r = foo_accumulator(some_seq)

instead of

  r = reduce(foo_function, some_seq)

regardless of whether some_seq is a regular list or a generator
expression.

So it seems to me that generator expressions have *no* effect on the
need or otherwise for reduce, and any suggestion to that effect should
be removed from the PEP as misleading and confusing.

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg at cosc.canterbury.ac.nz	   +--------------------------------------+