which methods to use?

[Alex Martelli]

Steven D'Aprano <steve at REMOVE.THIS.cybersource.com.au> wrote:
   ...
> In general:
> 
> - use a list comprehension when you need to calculate the list items
> 
> - use slicing when you are copying an actual list, or if you don't care
> what type of object you get
> 
> - use the list() function when your existing object might not be an actual
> list, and you want the copy to be a list.

Personally, I don't like the looks of:
    newlist = oldlist[:]

It's always looked more like Perl than Python to me.  I prefer:
    newlist = list(oldlist)

There may be a small performance hit (since Python must lookup the name
'list') but it's typically not important (save in extreme
bottlenecks:-).  It's way faster than copy.copy(oldlist), anyway:-)

I particularly like the way "calling the type for shallow copies" is
conceptually uniform across types, e.g.:

    newlist = list(oldlist)
    newdict = dict(olddict)
    newtuple = tuple(oldtuple)
    newset = set(oldset)

versus the mishmash one gets by using slicing for the sequences and
.copy() for the dict and set.

A matter of purely stylistic importance, of course.


Alex