copy list, which way is best? /style

[Andreas Kuntzagk]

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

 

[Andrew Wilkinson]

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

 

[Duncan Booth]

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:
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.
This will copy any object whether or not it is a sequence, but it may still
return the original object for immutables.
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).