My (late) beef with Simple Generator syntax (PEP 255)

[sismex01 at hebmex.com]

> From: Cameron Horn [mailto:camhorn at mac.com]
> Sent: Wednesday, November 13, 2002 4:26 PM
>  
> On Wednesday, Nov 13, 2002, at 02:19PM, <sismex01 at hebmex.com> wrote:
> 
> >> From: Cameron Horn [mailto:camhorn at mac.com]
> >> Sent: Wednesday, November 13, 2002 4:20 PM
> >>  
> >> On Wednesday, Nov 13, 2002, at 02:16PM, David Eppstein 
> >> <eppstein at ics.uci.edu> wrote:
> >> 
> >> >On 11/13/02 2:11 PM -0800 Cameron Horn <camhorn at mac.com> wrote:
> >> >>> What I wonder is, why does it need to be a generator?  
> >> What's wrong with
> >> >>> def foo(): return ( )
> >> >>> ?
> >> >>
> >> >> You're right if it's a one-time thing.  However, if I've got a
> >> >> scaffolding like this, then it matters.
> >> >>
> >> >> def process_generator(function):
> >> >>    for x in function():
> >> >>       print x
> >> >
> >> >How does the function foo() I defined above fail to work in this 
> >> >scaffolding?
> >> 
> >> In the "TypeError: iteration over non-sequence" sort of way.
> >>
> >
> >An empty tuple is a sequence also;
> >
> >the "return ( )" thing is returning an empty tuple,
> >not "None".  You can make it clearer by using
> >"return tuple()" rather than "return ()".
> 
> Oops.  Missed those parentheses.  Then it is completely 
> useful, unless you end up using the "next" method.
>

In that case, if you reckon you're going to use .next()
directly, then you should change 'foo' to something like
the following:

def foo(): return iter(tuple())

It's going to return a valid iterator which is going to
try to iterate through an empty tuple, so it's going
to raise StopIteration the first time you call .next().


HTH

-gustavo