Why no warnings when re-assigning builtin names?

[Seebs]

On 2011-08-17, Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:
> On Wed, 17 Aug 2011 01:17 pm Seebs wrote:
> [...]
>> "Another" scope is normally a horizontal thing -- you're talking about
>> a different scope such that you are *either* in this one *or* in that
>> one.

>> Built-ins are not in a scope you are never not in.

> That's technically incorrect. Built-ins are a scope you are never in, if
> by "in" you mean "code is executed in this scope".

No, by "in" I mean "lookups from your code will reach this scope if they
don't find something sooner".

>> Hmm.  See, I've never reached that, in Python or any other language.  I
>> figure it creates a new potential for confusion, and that I would rather
>> avoid any ambiguity.  I don't *like* ambiguity in code.

> Ah, well you see the thing is, this is Python. As soon as you call any
> function you don't control, you no longer know what your environment is
> with any certainty. For all you know, the harmless-looking function is
> monkey-patching builtins like there's no tomorrow. Speaking broadly,
> perhaps too broadly, we're incredibly proud of the ability to modify nearly
> everything at runtime.

Heh.

> Fortunately, while we are proud of having that ability, actually *using* it
> is considered a mortal sin. We're not Ruby developers -- if you actually
> monkey-patch something, especially built-ins, you can expect to be taken
> outside and slapped around with a fish if you get caught.

Okay, so.

Here's what I don't get.

If it's such a bad thing, *why is it allowed*?  Why are you proud of the
ability to do something that you are never socially-allowed to do?

I have mixed feelings about Ruby's general tolerance for monkey-patching,
although I've seen it do some pretty awesome things, so I am somewhat
inclined to accept that it may be worth it.  But it's clearly a feature
which is used intentionally.

It sounds to me like Python is very proud of having a feature which no
one would ever use.  ... Why?

> Sure. But they can't have that certainty regardless of whether you shadow
> something, because how do they know whether you've shadowed it or not?

Well, they could trust me.  :)

> In theory, anything could be anything at any time, and you have no
> protection. In practice, I worry more about being eaten by
> genetically-engineered flying piranhas than about rogue monkey-patching
> code.

I do too, if I know that people don't shadow built-ins.  If I know that
people are shadowing built-ins, then some of the time, when I'm editing
other peoples' code, they HAVE effectively monkey-patched it.

-s
-- 
Copyright 2011, all wrongs reversed.  Peter Seebach / usenet-nospam at seebs.net
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