Python List Issue

[Terry Reedy]

"Nick L" <Fearnot003 at mchsi.com> wrote in message 
news:ADu1e.23161$fn3.19315 at attbi_s01...
> I've hit a brick wall on something that I'm guessing is pretty simple but
> it's driving me nuts. I noticed that with python lists, generally when 
> you
> make a copy of a list (ie, List1 = List2)

Python is not C, etc.  Assigning a name to an object *never* makes a copy. 
Assigning a second name creates an alias.  Aliases are problems in any 
language that allows them (which C does also, via pointers).  Consider

Nick_PythonLearner = Nick_L

> List1 just becomes a reference to List2

Ditto for the two Nick names, but better said, both names refer to the same 
person (or list).

> and any modifications done to List1 affects List2.

and ditto for a person with more than one name -- which is almost everyone 
in the modern world (Nick, Mr. L, etc).

> Ok I can live with this

Good.  Name confusion is everywhere.

> but I want to make a completely seperate [sic] copy not attached to the
> original in anyway. So then I used this method. List1 = List2[:]

For a shallow (one level) copy, List1=list(List2) is now prefered.  For a 
deep (complete, all-level) copy, follow Kern's advice: copy.deepcopy.

Terry J. Reedy