What is a function parameter =[] for?

[fl]

On Wednesday, November 18, 2015 at 5:12:44 PM UTC-5, Ian wrote:
> On Wed, Nov 18, 2015 at 2:08 PM, fl <com> wrote:
> > Hi,
> >
> > I have tried the below function and find that it can remember the previous
> > setting value to 'val'. I think the second parameter has something on this
> > effect, but I don't know the name and function of '=[]' in this application.
> >
> > Could you explain a little to me?
> > Thanks,
> >
> >
> > def eList(val, list0=[]):
> >     list0.append(val)
> >     return list0
> > list1 = eList(12)
> > list1 = eList('a')
> 
> The list0 parameter has a default value, which is [], an initially
> empty list. The default value is evaluated when the function is
> defined, not when it is called, so the same list object is used each
> time and changes to the list are consequently retained between calls.

Thanks. The amazing thing to me is that the following two line codes:
list1 = eList(12) 
list2 = eList('a')

will have both list1 and list2 the same cascaded values:

list1
Out[2]: [12, 'a']

list2
Out[3]: [12, 'a']

I have known object concept in Python.
1. Why do they have the same list value?
 Function eList must be for this purpose?
2. If I want to have two separate lists, how to avoid the above result?
 Function eList is not for this purpose?

Thanks again.