On Fri, Oct 17, 2003 at 11:55:53AM -0600, Shane Holloway (IEEE) wrote:
mygenerator = x for x in S
for y in x for x in S: print y
return x for x in S
Interesting but potentially confusing: we could expect the last one to mean that we executing 'return' repeatedly, i.e. returning a value more than once, which is not what occurs.
I'm not sure what you mean by executing 'return' repeatedly; the closest thing in Python is returning a sequence, and this is pretty close (for many practical purposes, returning an iterator is just as good as returning a sequence).
Similarily,
yield x for x in g()
in a generator would be quite close to the syntax discussed some time ago to yield all the values yielded by a sub-generator g, but in your proposal it wouldn't have that meaning: it would only yield a single object, which happens to be an iterator with the same elements as g().
IMO this is not at all similar to what it suggests for return, as executing 'yield' multiple times *is* a defined thing. This is why I'd prefer to require extra parentheses; yield (x for x in g()) is pretty clear about how many times yield is executed.
Even with parenthesis, and assuming a syntax to yield from a sub-generator for performance reason, the two syntaxes would be dangerously close:
yield x for x in g() # means for x in g(): yield x yield (x for x in g()) # means yield g()
I don't see why we need yield x for x in g() when we can already write for x in g(): yield x This would be a clear case of "more than one way to do it". --Guido van Rossum (home page: http://www.python.org/~guido/)