"Diez B. Roggisch" <[EMAIL PROTECTED]> writes:
> [EMAIL PROTECTED] wrote:
>> The Example 2 builds a list, that is then thrown away. It's just a
>> waste of memory (and time).
> No, it doesn't. It uses append because it refers to itself in the
> if-expression. So the append(c) is needed - and thus the assignment
> possible but essentially useless.
Yes it does. A list comprehension *always* creates a list. In
this case it will be a list of None, since that is what list.append()
returns. See this:
>>> new=[]
>>> s="This is a foolish use of list comprehensions"
>>> [ new.append(c) for c in s if c not in new ]
[None, None, None, None, None, None, None, None, None, None, None,
None, None, None, None, None, None]
Yes, you do get a correct result in 'new', but you *also* create
a 17 long list with all elements set to None, that is immediately
thrown away.
--
Thomas Bellman, Lysator Computer Club, Linköping University, Sweden
"I refuse to have a battle of wits with an ! bellman @ lysator.liu.se
unarmed person." ! Make Love -- Nicht Wahr!
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