On Wed, Jun 2, 2010 at 10:40 AM, pmz <przemek.zaw...@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 -- http://mail.python.org/mailman/listinfo/python-list
