Re: assignment in a for loop
- From: Ben Finney <bignose+hates-spam@xxxxxxxxxxxxxxx>
- Date: Wed, 17 May 2006 15:05:29 +1000
"MackS" <mackstevenson@xxxxxxxxxxx> writes:
... i = i + 1l = [1,2]
for i in l:
...
[1, 2]l
I understand (I think!) that this is due to the fact that in Python
what looks like "assignment" really is binding a name to an
object. The result is that inside the loop I am creating an object
with value (i+1) and then "pointing" the name i at it. Therefore,
the object to which i previously pointed (an element of list l)
remains unchanged.
That's a fair explanation, yes.
Two brief questions:
1) Is what I wrote above (minimally) correct?
Correct for what? You can tell if it's *syntactically* correct by
simply running it.
As for any other "correct", define that. Does it do what you want it
to do?
2) Independently of the answer to 1, is there a way for me to assign
to elements of a list inside a loop and without resorting to C-style
ugliness of
for i in range(len(l))
l[i] = l[i] + 1
You can build a new list from your operations on the old one.
new_list = []
for x in old_list:
new_list.append(x+1)
You can also do it more succinctly with a list comprehension
expression.
(Note: not using a list comprehension.)
What's preventing the use of list comprehensions?
new_list = [x+1 for x in old_list]
--
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Ben Finney
.
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