On Oct 7, 4:10 pm, Rogério Brito <rbr...@ime.usp.br> wrote:
[snip]
>
> v = [0 for i in range(20)]
>
> v = [0] * 20
>
> v = []
> for i in range(20): v.append(0)
>
> What should I prefer? Any other alternative?
The Pythonic way is to not to preinitialize the list at all. Don't
put anything in the list until you have the data you need.
> If possible, I would like to simply declare the list and fill it latter in my
> program, as lazily as possible (this happens notoriously when one is using a
> technique of programming called dynamic programming where initializing all
> positions of a table may take too much time in comparison to the filling of
> the
> array).
So, if I understand you, you are thinking of your list as a table with
dynamically calculated entries, and want to calculate the entries upon
request.
Three possibilities:
1. Initialize the list using v = [None]*n (I recomment using None
instead of 0 for this, in most cases)
2. Use a dict instead. Dict items pop into existence if you assign
with a key that doesn't exist.
v = {}
Then you can do
v[1] = a
v[10] = n
v[999] = c
3. Consider numpy, which allows preallocation of lists:
v = np.zeros(100)
[snip]
> For instance, if I
> define:
>
> class C:
> f = 1
> def g(self):
> return f
>
> I get an annoying message when I try to call the g method in an object of type
> C, telling me that there's no global symbol called f. If I make g return
> self.f
> instead, things work as expected, but the code loses some readability.
>
> Is there any way around this or is that simply "a matter of life"?
Matter of life. It's that way by design.
Carl Banks
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