Dangerous behavior of list(generator)

[Peter Otten]

Terry Reedy wrote:

> On 12/13/2009 11:33 PM, exarkun at twistedmatrix.com wrote:
>> This could provide behavior roughly equivalent to the behavior
>> of a list comprehension.
> 
> Impossible. The only serious option for consistency is to special case
> list comps to also trap StopIteration raised in the expression part, but
> the devs decided not to do this as doing do is arguably a bug.

A viable option might be to introduce a different exception type and 
translate

(expr(v) for v in items if cond(v))

into

def gen(items, expr, cond):
    for v in items:
        try:
            if cond(v):
                yield expr(v)
        except StopIteration:
            raise TypeError("StopIteration raised in "
                            "'expr' or 'cond' part of "
                            "a generator expression")
 
Peter