What is a function parameter =[] for?

[fl]

On Wednesday, November 18, 2015 at 7:15:05 PM UTC-5, Chris Angelico wrote:
> On Thu, Nov 19, 2015 at 11:02 AM, Ian Kelly <ian.g.kelly at gmail.com> wrote:
> > On Wed, Nov 18, 2015 at 4:22 PM, Chris Angelico <rosuav at gmail.com> wrote:
> >> On Thu, Nov 19, 2015 at 10:14 AM, BartC <bc at freeuk.com> wrote:
> >>> So, looking at some source code, a default value for certain types is only
> >>> certain to be that value for the very first call of that function?
> >>
> >> On the contrary, it is certain always to be that exact object.
> >
> > "Certain" may be a bit overly strong.
> >
> >>>> def f(x=42):
> > ...   return x
> > ...
> >>>> f()
> > 42
> >>>> f.__defaults__ = (43,)
> >>>> f()
> > 43
> 
> I'll raise you one.
> 
> >>> def f(x=42):
> ...     return x
> ...
> >>> f()
> 42
> >>> import ctypes
> >>> ctypes.c_int.from_address(id(43)+ ctypes.sizeof(ctypes.c_size_t) + ctypes.sizeof(ctypes.c_voidp)).value=42
> >>> f.__defaults__ = (43,)
> >>> f()
> 42
> >>>
> 
> Nothing is certain in Python. And two wrongs can make a... hmm... no,
> this is not a right. It is not a privilege either. It is a dastardly
> trick played on people's minds.
> 
> ChrisA

After I try with

list1 = eList(12, [2])

and

list1 = eList(12)

it gives me new surprises. Even though I delete list1, the subsequent
list1 = eList(12)
will remember the number of '12' of the previous sequence. This is my new
question: What does 'del' do? It does not look like a thorough list deletion
 from the effect.

Thanks,

.....................
list1 = eList(12, [2])

list1
Out[57]: [2, 12]

list1 = eList(12)

list1
Out[59]: [12, 12, 12]

list1 = eList(12, [2])

list1
Out[61]: [2, 12]

list1 = eList(12, [2])

list1
Out[63]: [2, 12]

list1 = eList(12, [2])

list1
Out[65]: [2, 12]

list1 = eList(12)

list1
Out[67]: [12, 12, 12, 12]

list1 = eList(12)

list1
Out[69]: [12, 12, 12, 12, 12]

list1 = eList(12, [2])

list1
Out[71]: [2, 12]

list1 = eList(12)

list1
Out[73]: [12, 12, 12, 12, 12, 12]

del list1

list1 = eList(12, [2])

list1 = eList(12)

list1
Out[77]: [12, 12, 12, 12, 12, 12, 12]