[Python-ideas] proposed methods: list.replace / list.indices

[MRAB]

On 2012-12-30 03:25, David Kreuter wrote:
> Hi python-ideas.
>
> I think it would be nice to have a method in 'list' to replace certain
> elements by others in-place. Like this:
>
>      l = [x, a, y, a]
>      l.replace(a, b)
>      assert l == [x, b, y, b]
>
> The alternatives are longer than they should be, imo. For example:
>
>      for i, n in enumerate(l):
>          if n == a:
>              l[i] = b
>
> Or:
>
>      l = [b if n==a else n for n in l]
>
> And this is what happens when someone tries to "optimize" this process.
> It totally obscures the intention:
>
>      try:
>          i = 0
>          while i < len(l):
>              i = l.index(a, i)
>              l[i] = b
>              i += 1
>      except ValueError:
>          pass
>
> If there is a reason not to add '.replace' as built-in method, it could
> be implemented in pure python efficiently if python provided a version
> of '.index' that returns the index of more than just the first
> occurrence of a given item. Like this:
>
>      l = [x, a, b, a]
>      for i in l.indices(a):
>          l[i] = b
>
> So adding .replace and/or .indices… Good idea? Bad idea?
>
What's your use-case?

I personally can't remember ever needing to do this (or, if I have, it
was so long ago that I can't remember it!).

Features get added to Python only when someone can show a compelling
reason for it and sufficient other people agree.