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Re: Drowning in a teacup?

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Give this a shot

    def snap(keyword, words):
        matches = [i for i, s in enumerate(words) if s.startswith(keyword)]
        for i in matches:
            lst.insert(0, lst.pop(i))

Your current implementation is reassigning the local variable ``mylist`` to
a new list inside the function.

On Fri, Apr 1, 2016 at 4:30 PM Fillmore <fillmore_remove@hotmail.com> wrote:

>
> notorious pass by reference vs pass by value biting me in the backside
> here. Proceeding in order.
>
> I need to scan a list of strings. If one of the elements matches the
> beginning of a search keyword, that element needs to snap to the front
> of the list.
> I achieved that this way:
>
>
>     for i in range(len(mylist)):
>          if(mylist[i].startswith(key)):
>              mylist = [mylist[i]] + mylist[:i] + mylist[i+1:]
>
> Since I need this code in multiple places, I placed it inside a function
>
> def bringOrderStringToFront(mylist, key):
>
>      for i in range(len(mylist)):
>          if(mylist[i].startswith(key)):
>              mylist = [mylist[i]] + mylist[:i] + mylist[i+1:]
>
> and called it this way:
>
>   if orderstring:
>       bringOrderStringToFront(Tokens, orderstring)
>
> right?
> Nope, wrong! contrary to what I thought I had understood about how
> parameters are passed in Python, the function is acting on a copy(!) and
> my original list is unchanged.
>
> I fixed it this way:
>
> def bringOrderStringToFront(mylist, key):
>
>      for i in range(len(mylist)):
>          if(mylist[i].startswith(key)):
>              mylist = [mylist[i]] + mylist[:i] + mylist[i+1:]
>      return(mylist)
>
> and:
>
> if orderstring:
>     Tokens = bringOrderStringToFront(Tokens, orderstring)
>
> but I'm left with a sour taste of not understanding what I was doing
> wrong. Can anyone elaborate? what's the pythonista way to do it right?
>
> Thanks
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>

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Thread

Drowning in a teacup? Fillmore <fillmore_remove@hotmail.com> - 2016-04-01 16:27 -0400
  Re: Drowning in a teacup? Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2016-04-01 20:39 +0000
    Re: Drowning in a teacup? Ian Kelly <ian.g.kelly@gmail.com> - 2016-04-01 14:52 -0600
  Re: Drowning in a teacup? MRAB <python@mrabarnett.plus.com> - 2016-04-01 21:45 +0100
  Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-01 20:46 +0000
  Re: Drowning in a teacup? Steven D'Aprano <steve@pearwood.info> - 2016-04-02 09:46 +1100
  Re: Drowning in a teacup? Fillmore <fillmore_remove@hotmail.com> - 2016-04-02 00:03 -0400
  Re: Drowning in a teacup? Vito De Tullio <vito.detullio@gmail.com> - 2016-04-02 07:45 +0200
  Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-02 05:51 +0000
  Re: Drowning in a teacup? Vito De Tullio <vito.detullio@gmail.com> - 2016-04-02 08:26 +0200
  Re: Drowning in a teacup? Peter Otten <__peter__@web.de> - 2016-04-02 12:31 +0200
  Re: Drowning in a teacup? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-04-02 12:53 +0100
  Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-02 14:36 +0000
  Re: Drowning in a teacup? Ned Batchelder <ned@nedbatchelder.com> - 2016-04-02 12:28 -0700
    Re: Drowning in a teacup? Random832 <random832@fastmail.com> - 2016-04-02 15:54 -0400
      Re: Drowning in a teacup? Steven D'Aprano <steve@pearwood.info> - 2016-04-03 12:33 +1000
    Re: Drowning in a teacup? Ethan Furman <ethan@stoneleaf.us> - 2016-04-02 16:15 -0700
    Re: Drowning in a teacup? Random832 <random832@fastmail.com> - 2016-04-02 19:19 -0400

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