PEP 289: Generator Expressions (please comment)

[Holger Krekel]

Raymond Hettinger wrote:
> Peter Norvig's creative thinking triggered renewed interest in PEP 289.
> That led to a number of contributors helping to re-work the pep details
> into a form that has been well received on the python-dev list:
> 
>     http://www.python.org/peps/pep-0289.html
> 
> In brief, the PEP proposes a list comprehension style syntax for
> creating fast, memory efficient generator expressions on the fly:
> 
>     sum(x*x for x in roots)
>     min(d.temperature()*9/5 + 32 for d in days)
>     Set(word.lower() for word in text.split() if len(word) < 5)
>     dict( (k, somefunc(k)) for k in keylist )
>     dotproduct = sum(x*y for x,y in itertools.izip(xvec, yvec))
>     bestplayer, bestscore = max( (p.score, p.name) for p in players )

Although most people on python-dev and here seems to like this PEP I
think it generally decreases readability.  The above constructs seem
heavy and difficult to parse and thus i am afraid that they interfere
with the perceived simplicity of Python's syntax. 

Sometimes it seems that introducing new syntax happens much easier 
than improving or adding stdlib-modules. 

> Each of the above runs without creating a full list in memory,
> which saves allocation time, conserves resources, and exploits
> cache locality.

I do like these properties, though :-)

At least I hope that generator expressions will only be introduced 
via a __future__ statement in Python 2.4 much like it happened with
'yield' and generators.  Maybe the PEP should have an "implementation
plan" chapter mentioning such details? 

cheers,

    holger