On 03/31/2015 09:18 AM, Albert van der Horst wrote:
In article <55062bda$0$12998$c3e8da3$54964...@news.astraweb.com>,
Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote:
The biggest difference is syntactic. Here's an iterator which returns a
never-ending sequence of squared numbers 1, 4, 9, 16, ...
class Squares:
def __init__(self):
self.i = 0
def __next__(self):
self.i += 1
return self.i**2
def __iter__(self):
return self
You should give an example of usage. As a newby I'm not up to
figuring out the specification from source for
something built of the mysterious __ internal
thingies.
(I did experiment with Squares interactively. But I didn't get
further than creating a Squares object.)
He did say it was an iterator. So for a first try, write a for loop:
class Squares:
def __init__(self):
self.i = 0
def __next__(self):
self.i += 1
return self.i**2
def __iter__(self):
return self
for i in Squares():
print(i)
if i > 50:
break
print("done")
Here's the same thing written as a generator:
def squares():
i = 1
while True:
yield i**2
i += 1
Four lines, versus eight. The iterator version has a lot of boilerplate
(although some of it, the two-line __iter__ method, could be eliminated if
there was a standard Iterator builtin to inherit from).
--
DaveA
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