MRAB schrieb:
Diez B. Roggisch wrote:
Dr Mephesto wrote:
Hi,
Im new to python, and OOP, and am trying to get a handle on list
comprehension.
Say I have a class Foo with a property called bar:
class Foo:
def __init__(self):
self.bar = random.randint(1,100)
and then I make a list of these objects:
Newlist = []
for x in range(10):
Newlist.append(Foo())
Now, suppose I wanted to triple the value of 'bar', I could always do:
for x in range(10):
Newlist[x].bar = Newlist[x].bar * 3
but can I do this using list comprehension? Thanks in Advance!
No, as such, because list-comprehensions require you to have an
*expression*
in front of the iteration:
resultlist = [<expr> for <variable(s)> in <iterable>]
Now what you of course can do is this:
def multiply(item):
item.bar = item.bar * 3
[multiply(i) for i in items]
However, doing this will make python produce a list of None-references -
which is a waste. It's up to you if you care about that, but generally it
is frowned upon because of that, and the fact that the conciseness of the
list-comp here isn't really helping with the readability.
If you had:
def multiply(item):
item.bar = item.bar * 3
return item
then:
[multiply(i) for i in items]
would return items. Still a bad idea, though, because you're using a
list comprehension for its side-effect.
And redundant, which was the reason I ommited it.
Diez
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