Chris Angelico wrote:
> On Sat, Feb 15, 2014 at 6:27 PM, Ian Kelly <[email protected]> wrote:
>> On Fri, Feb 14, 2014 at 8:31 PM, Nick Timkovich <[email protected]>
>> wrote:
>>> OK, now the trick; adding `data = None` inside the generator works, but
>>> in my actual code I wrap my generator inside of `enumerate()`, which
>>> seems to
>>> obviate the "fix". Can I get it to play nice or am I forced to count
>>> manually. Is that a feature?
>>
>> Yeah, looks like enumerate also doesn't release its reference to the
>> previous object until after it gets the next one. You'll just have to
>> make do without.
>
> You could write your own enumerate function.
>
> def enumerate(it, i=0):
> it = iter(it)
> while True:
> yield i, next(it)
> i += 1
>
> That shouldn't keep any extra references around.
An alternative approach ist to yield weak refs and thus have the generator
control the object lifetime. This doesn't work with the built-in list type
though:
import weakref
try:
from itertools import imap # py2
except ImportError:
imap = map # py3
N = 0
def log_deleted(*args):
global N
N -= 1
print("deleted, new N: {}".format(N))
def log_created():
global N
N += 1
print("created, new N: {}".format(N))
def weakrefs(f):
def weakrefs(*args, **kw):
return imap(lambda x: weakref.proxy(x, log_deleted), f(*args, **kw))
return weakrefs
class List(list):
def __str__(self):
s = str(self[:5])
if len(self) > 10:
s = s[:-1] + ", ... ]"
return s
@weakrefs
def biggen():
sizes = 1, 1, 10, 1, 1, 10, 10, 1, 1, 10, 10, 20, 1, 1, 20, 20, 1, 1
for size in sizes:
data = List([1] * int(size * 1e4))
log_created()
yield data
data = None
if __name__ == "__main__":
for i, x in enumerate(biggen()):
print("{} {}".format(i, x))
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