bokr at oz.net
Mon Nov 1 08:20:51 CET 2004
On Mon, 01 Nov 2004 03:11:42 GMT, exarkun at divmod.com wrote:
>On Sun, 31 Oct 2004 19:00:07 GMT, bokr at oz.net (Bengt Richter) wrote:
>> BTW, will anything that works in a list comprehension work in a generator expression
>> (assuming one does not depend on the generator expression having leftover outside
>> side effect bindings like the LC version)?
> Nope. For example, I don't think the code in this thread will work if converted to a generator expression. A simplified example:
> >>> x = 0
> >>> list(x for x in iter(lambda: x + 1, 4))
> ( runs forever, so C-c )
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> File "<stdin>", line 1, in <generator expression>
> >>> [x for x in iter(lambda: x + 1, 4)]
> [1, 2, 3]
> `x' in the lambda in the list comprehension resolves to a different name than `x' in the generator comprehension.
I had a sneaky suspicion that it _could_ be so, hoping not. But your example doesn't play fair
because you don't give x an initial condition inside the scope of the expression. E.g.,
>>> [x for x in  for x in iter(lambda:x+1, 4)]
[1, 2, 3]
>>> list(x for x in  for x in iter(lambda:x+1, 4))
File "<stdin>", line 1
list(x for x in  for x in iter(lambda:x+1, 4))
SyntaxError: invalid syntax
Well, I don't have 2.4 yet, but what does it do?
If the generator expression scope causes a closure access from lambda it should be ok, IWT.
More information about the Python-list