On 2013-03-06 22:20, Roy Smith wrote:
> I stumbled upon an interesting bit of trivia concerning lists and
> list comprehensions today.
I agree with Dave Angel that this is interesting. A little testing
shows that this can be rewritten as
my_objects = list(iter(my_query_set))
which seems to then skip the costly __len__ call. Performance geeks
are welcome to time it against the list-comprehension version :-)
-tkc
class Foo(object):
def __init__(self):
self.items = range(10)
def __iter__(self):
return iter(self.items)
def __len__(self):
print "Calling costly __len__"
return len(self.items)
print "Ensuring we can iterate over it:"
for x in Foo():
print x
print "\nJust call list():"
lst = list(Foo())
print lst
print "\nCall list(iter())"
lst = list(iter(Foo()))
print lst
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