[Tutor] to place all zeros of an existing list in the starting of a new list

[Bryan Karsh]

I too enjoy Mr. Singh’s questions. He’s asking what I often ask myself
while I code: “This approach works… but is it optimal? Am I introducing a
good or bad habit doing it this way?”

On Sun, May 30, 2021 at 6:31 PM boB Stepp <robertvstepp at gmail.com> wrote:

> On Sun, May 30, 2021 at 7:40 PM dn via Tutor <tutor at python.org> wrote:
> >
> >
> >
> > On 31/05/2021 11.56, Manprit Singh wrote:
> > > Dear sir ,
> > > Consider a list ls = [2, 5, 0, 9, 0, 8], now i have to generate a new
> list
> > > from this existing list , new list must contain all zeros in the
> starting,
> > > all other elements of the existing list must be placed after zeros in
> new
> > > list . So new list must be :
> > > new = [0, 0, 2, 5, 9, 8]
> > >
> > > The way I am doing it is :
> > >>>> ls = [2, 5, 0, 9, 0, 8]
> > >>>> sorted(ls, key=lambda x: x != 0)
> > > [0, 0, 2, 5, 9, 8]
> > >>>>
> > > Is this the correct way ? or is there something better that can be
> done ?
> >
> > +1 @Alan's comment.
> > These appear highly academic questions with little apparent real-world
> > application.
>
> Or is Mr. Singh simply trying to understand the fine details of how
> Python does things by coming up with these examples and exploring
> them? I suspect that much exploration may have occurred (Which we
> never get to see) before submitting his question with the intent of
> getting validation of his conclusions. In any case, I found his
> example quite stimulating.  I realized that I did not understand how
> the "key" keyword parameter worked in sorted(),  when I did not see
> how he got the result he had.  Of course I have not yet had any use
> for that optional parameter.  I finally realized after playing around
> in the interpreter and going to the docs multiple times that the key
> function mapped each element in the original result to the following:
> [2, 5, 0, 9, 0, 8] => [True, True, False, True, False, True], then
> sorted this "Boolean" list where I had to keep in mind for sorting
> purposes that False = 0 and True = 1.  Then sorted() apparently uses
> this new order to reverse the mapping to get the end result of [0, 0,
> 2, 5, 9, 8].
>
> So Mr. Singh's question caused me to learn multiple things tonight and
> I am grateful to him!
>
> Cheers!
> boB Stepp
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