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copy list, which way is best? /style

Hi,

There are three ways to (shallow)copy a list l I'm aware of:
l2=list(l)
l2=l[:]
l2.copy.copy(l)


Are there any differences? Are there more (reasonable) ways?
I think the first is the most pythonic, second looks more like this other
p-language and third requires an import, so I would prefer the first.
Do you agree?

Andreas
Jul 18 '05 #1
2 35765
Andreas Kuntzagk wrote:
Hi,

There are three ways to (shallow)copy a list l I'm aware of:
l2=list(l)
l2=l[:]
l2.copy.copy(l)


Are there any differences? Are there more (reasonable) ways?
I think the first is the most pythonic, second looks more like this other
p-language and third requires an import, so I would prefer the first.
Do you agree?

Andreas


The way I'd do it is

from copy import copy
l2 = copy(l1)

or

from copy import deepcopy
l2 = deepcopy(l1)

I don't know what the difference is, if any, but I think this way is more
readable.

HTH,
Andrew Wilkinson

--
Study + Hard Work + Loud Profanity = Good Code
Jul 18 '05 #2
"Andreas Kuntzagk" <an************ **@mdc-berlin.de> wrote in
news:be******** ****@fu-berlin.de:
There are three ways to (shallow)copy a list l I'm aware of:
l2=list(l)
l2=l[:]
l2.copy.copy(l)
Are there any differences? Are there more (reasonable) ways?
I think the first is the most pythonic, second looks more like this other
p-language and third requires an import, so I would prefer the first.
Do you agree?


They all do slightly different things.
I think this is a fairly accurate description of what each of these does:
l2 = list(l) This will copy any iterable object and will produce a new, distinct list as
a result.
l2=l[:] This will copy a sequence, and will return an object of the same type as
the original. If the original is immutable, then it may simply return the
original object and not bother with making a copy.
l2=copy.copy(l) This will copy any object whether or not it is a sequence, but it may still
return the original object for immutables.
l2=copy.deepcop y(l)

This will make a deep copy of an object. It only returns the original
object for immutables if any objects they contain are also immutable
(including their contents).

--
Duncan Booth du****@rcp.co.u k
int month(char *p){return(1248 64/((p[0]+p[1]-p[2]&0x1f)+1)%12 )["\5\x8\3"
"\6\7\xb\1\x9\x a\2\0\4"];} // Who said my code was obscure?
Jul 18 '05 #3

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