On 5/4/05, Nick Coghlan <ncoghlan at gmail.com> wrote:
> With single-pass semantics, an iterator used in a block statement would have
> it's .next() method called exactly once, and it's __exit__ method called exactly
> once if the call to .next() does not raise StopIteration. And there's no need to
> mess with the meaning of break, return or continue - they behave as usual,
> affecting the surrounding scope rather than the block statement.
>
> The only new thing needed is an __exit__ method on generators (and the block
> syntax itself, of course).
Makes me wonder if we shouldn't just return to the __enter__() and
__exit__() names of PEP 310[1] where for a generator __enter__() is
just an alias for next(). We could even require Phillip J. Eby's
"blockgenerator" decorator to rename next() to __enter__(), and add
the appropriate __exit__() method. Something like:
class blockgen(object):
def __init__(self, gen):
self.gen = gen
def __enter__(self):
self.gen.next()
def __exit__(self):
# cause finally blocks to be executed
def blockgenerator(genfunc):
def getblockgen(*args, **kwargs):
return blockgen(genfunc(*args, **kwargs))
return getblockgen
to be used like:
@blockgenerator
def locking(lock):
lock.acquire()
try:
yield
finally:
lock.release()
'Course, it might be even nicer if try/finally around a yield could
only be used with block generators... To get a syntax error, we'd
have to replace the decorator with a new syntax, e.g. Tim Delaney's
"resource" instead of "def" syntax or maybe using something like
"blockyield" or "resourceyield" instead of "yield" (though these are
probably too long)...
Steve
[1]http://www.python.org/peps/pep-0310.html
--
You can wordify anything if you just verb it.
--- Bucky Katt, Get Fuzzy
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