Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Michael Selik <michael.selik@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Drowning in a teacup?
Date: Fri, 01 Apr 2016 20:46:19 +0000
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Message-ID: <mailman.332.1459543597.28225.python-list@python.org>
References: <ndmlj2$pb0$1@gioia.aioe.org>
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Xref: csiph.com comp.lang.python:106262

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
>