On Oct 14, 7:08 pm, Paul Rubin <no.em...@nospam.invalid> wrote:
> Steven D'Aprano <st...@remove-this-cybersource.com.au> writes:
> > (4) Expensive generators. The beauty of generators is that they produce
> > values on demand. Making all generators cache their first value means
> > that you pay that cost even if you end up never needing the first value.
>
> You wouldn't generate the cached value ahead of time. You'd just
> remember the last generated value so that you could use it again.
> Sort of like getc/ungetc.
>
> An intermediate measure might be to have a stdlib wrapper that added
> caching like this to an arbitrary generator. I've written such things a
> few times in various clumsy ways. Having the caching available in the C
> code would eliminate a bunch of indirection.
Is there an idiomatic way in Python to wrap a generator with a getc/
ungetc mechanism?
I know Paul is not alone in having written such things himself in
various clumsy ways.
This is my own clumsy attempt, but it seems like there should be a
simpler way to achieve what I'm doing.
def abc():
yield 'a'
yield 'b'
yield 'c'
for letter in abc():
print letter
class Wrap:
def __init__(self, g):
self.g = g
self.use_cached = False
def get(self):
if self.use_cached:
self.use_cached = False
return self.value
self.value = self.g.next()
return self.value
def unget(self):
if self.use_cached:
raise Exception('only one unget allowed')
self.use_cached = True
w = Wrap(abc())
print w.get()
w.unget()
print w.get()
print w.get()
for letter in w.g:
print letter
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