Syntax question

[Matteo Landi]

Yes it is; d[i:j] is equal to "give me the array from the d[i] to d[j
- 1]", and if you omit i and j then the i and j are respectively
assumed as 0 and len(d) - 1.

On Wed, Jun 2, 2010 at 8:01 PM, pmz <przemek.zawada at gmail.com> wrote:
> On 2 Cze, 19:56, geremy condra <debat... at gmail.com> wrote:
>> On Wed, Jun 2, 2010 at 10:40 AM, pmz <przemek.zaw... at gmail.com> 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.
> --
> http://mail.python.org/mailman/listinfo/python-list
>



-- 
Matteo Landi
http://www.matteolandi.net/