Syntax question

[pmz]

Dear Group,

It's really rookie question, but I'm currently helping my wife in some
python-cases, where I'm non-python developer and some of syntax-diffs
make me a bit confused.

Could anyone give some light on line, as following:
"ds = d[:]"  ### where 'd' is an array

Let me guess, is it a declaration of two-dimension array?

Thanks a lot for help and all the best,
Przemek M. Zawada
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Re: Syntax question

[pmz]

On 2 Cze, 19:56, geremy condra  wrote:
> On Wed, Jun 2, 2010 at 10:40 AM, pmz  wrote:
> > Dear Group,
>
> > It's really rookie question, but I'm currently helping my wife in some
> > python-cases, where I'm non-python developer and some of syntax-diffs
> > make me a bit confused.
>
> > Could anyone give some light on line, as following:
> > "ds = d[:]"  ### where 'd' is an array
>
> I'm guessing you mean that d is a list. The square
> braces with the colon is python's slicing notation,
> so if I say [1,2,3,4][0] I get a 1 back, and if I say
> [1,2,3,4][1:4] I get [2,3,4]. Python also allows a
> shorthand in slicing, which is that if the first index
> is not provided, then it assumes 0, and that if the
> second index is not provided, it assumes the end
> of the list. Thus, [1,2,3,4][:2] would give me [1,2]
> and [1,2,3,4][2:] would give me [3, 4]. Here, neither
> has been provided, so the slice simply takes the
> items in the list from beginning to end and returns
> them- [1,2,3,4][:] gives [1,2,3,4].
>
> The reason someone would want to do this is
> because lists are mutable data structures. If you
> fire up your terminal you can try the following
> example:
>
> >>> a = [1,2,3,4]
> >>> b = a
> >>> c = [:]
> >>> b[0] = 5
> >>> b
> [5,2,3,4]
> >>> # here's the issue
> >>> a
> [5,2,3,4]
> >>> # and the resolution
> >>> c
>
> [1,2,3,4]
>
> Hope this helps.
>
> Geremy Condra

Thank you for such fast answer! I quite catch, but:
As I see, the d[:] is equal to sentence "get the d array from the
first to the last element"? :)

P.
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Re: Syntax question

[pmz]

On 2 Cze, 20:07, Matteo Landi  wrote:
> Anyway I suggest you to use a syntax like:
>
> >>>b = list(a)
>
> in order to copy a list, it should be better than slicing.
>
>
>
>
>
> On Wed, Jun 2, 2010 at 7:56 PM, geremy condra  wrote:
> > On Wed, Jun 2, 2010 at 10:40 AM, pmz  wrote:
> >> Dear Group,
>
> >> It's really rookie question, but I'm currently helping my wife in some
> >> python-cases, where I'm non-python developer and some of syntax-diffs
> >> make me a bit confused.
>
> >> Could anyone give some light on line, as following:
> >> "ds = d[:]"  ### where 'd' is an array
>
> > I'm guessing you mean that d is a list. The square
> > braces with the colon is python's slicing notation,
> > so if I say [1,2,3,4][0] I get a 1 back, and if I say
> > [1,2,3,4][1:4] I get [2,3,4]. Python also allows a
> > shorthand in slicing, which is that if the first index
> > is not provided, then it assumes 0, and that if the
> > second index is not provided, it assumes the end
> > of the list. Thus, [1,2,3,4][:2] would give me [1,2]
> > and [1,2,3,4][2:] would give me [3, 4]. Here, neither
> > has been provided, so the slice simply takes the
> > items in the list from beginning to end and returns
> > them- [1,2,3,4][:] gives [1,2,3,4].
>
> > The reason someone would want to do this is
> > because lists are mutable data structures. If you
> > fire up your terminal you can try the following
> > example:
>
> >>>> a = [1,2,3,4]
> >>>> b = a
> >>>> c = [:]
> >>>> b[0] = 5
> >>>> b
> > [5,2,3,4]
> >>>> # here's the issue
> >>>> a
> > [5,2,3,4]
> >>>> # and the resolution
> >>>> c
> > [1,2,3,4]
>
> > Hope this helps.
>
> > Geremy Condra
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
> --
> Matteo Landihttp://www.matteolandi.net/

In fact, that ain't my syntax, I'd rather use C++ for that project,
because that's my world is not Python, but thank you anyway for help -
I see that Python also has many fans and friends online :) I'll try
help her using your explanations.

THANK you again and all the best,
Przemek M. Zawada

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