2008/4/26 Alexander Belopolsky <[EMAIL PROTECTED]>:
> > What is range()?
> >
> > help(range) shows me that range "Returns an iterator that generates
> > the numbers in the range on demand."
>
> This is not correct in 3.x: range does not return an iterator. There is an
> iterator similar to range in itertools: count. I would not mind adding
> optional step and stop arguments to it.
I took that string doing help(range) in the py3k branch, r62509, is it a bug?
Which should the range() definition be, in your words?
> > Ahá! So, as ints are unbound in Python, I could easily do:
> >
> > >>> r = range(1,1000000000000000000000)
>
> The problem with supporting this is that len(r) will raise overflow error.
> It would be nice to get rid of the limitation on len(), but it will be hard
> and may not be possible to do efficiently.
Maybe len() should be removed? Maybe indexing? I don't know: I don't
know what range() is. I mean, I took the previous definition from the
actualy Py3k, but you say it's wrong.
I think that we should first define the range() semantic, what is core
to it and what would be a nice thing to have but is not mandatory, and
then try to comply.
At this moment I stopped writing this mail, and I went to code a
Range() class to have the semantics that we're seeking here (it's
attached), and I couldn't finish it 100% because of a len() behaviour
that I'm including here, because it's related to what we're discussing
here:
>>> class C:
... def __len__(self):
... return 100000000000000000000000000000
...
>>> c = C()
>>> len(c)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OverflowError: Python int too large to convert to C ssize_t
>From an external point of view, and knowing that ints are unbound, why
should I have an error here?
Thanks!
--
. Facundo
Blog: http://www.taniquetil.com.ar/plog/
PyAr: http://www.python.org/ar/
class Range:
def __init__(self, frm=None, to=None, step=None):
if to is None:
self.frm = 0
self.to = frm
else:
self.frm = frm
self.to = to
if step is None:
self.step = 1
else:
self.step = step
print(self.frm, self.to, self.step)
self.point = self.frm
def __iter__(self):
return self.__next__()
def __next__(self):
while True:
if self.step > 0 and self.point >= self.to:
break
if self.step < 0 and self.point <= self.to:
break
yield self.point
self.point += self.step
def __len__(self):
lim = self.to - self.frm
d, r = divmod(lim, self.step)
if r:
d += 1
return d
def __getitem__(self, pos):
return self.frm + self.step * pos
if __name__ == "__main__":
r = Range(6)
assert list(r) == [0, 1, 2, 3, 4, 5]
assert len(r) == 6
assert r[2] == 2
r = Range(2, 9)
assert list(r) == [2, 3, 4, 5, 6, 7, 8]
assert len(r) == 7
assert r[2] == 4
r = Range(2, 9, 2)
assert list(r) == [2, 4, 6, 8]
assert len(r) == 4
assert r[2] == 6
r = Range(13, 4, -2)
assert list(r) == [13, 11, 9, 7, 5]
assert len(r) == 5
assert r[2] == 9
r = Range(1000000000000000000000)
assert r[2] == 2
assert len(r) == 1000000000000000000000
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