[Tutor] lists of lists: more Chutes & Ladders!

[eryksun]

On Tue, Dec 31, 2013 at 10:53 PM, Steven D'Aprano <steve at pearwood.info> wrote:
>
> __builtins__ with-an-s is a crappy hack that has never worked correctly
> and has caused more confusion than help:
>
> https://mail.python.org/pipermail/python-3000/2007-March/006170.html
>
> "Restricted mode" in CPython has never worked correctly, __builtins__
> has always been an implementation-specific detail, and you should never
> use it. The one you actually want is "__builtin__" (no "s") in Python 2,
> or "builtins" (no underscores) in Python 3.

But I didn't say to use the "__builtins__" module.  __builtin__ works
in Jython, but the module I referenced was "builtins", per the 3.x
example given by Denis.

I'm definitely not talking about the weird hack that __builtins__ is a
module in __main__ in CPython. I've never understood the reason for
that, and I loathe it. In every other module it's a dict:

    >>> d = {}
    >>> exec("x = 1", d)
    >>> type(d['__builtins__'])
    <class 'dict'>

I'm not familiar with the implementation of Jython's builtins
namespace. Using the name __builtins__ was based on CPython. Just to
be clear, I'm talking about the builtins namespace and scope --
however it's implemented in Jython or IronPython. I don't use them and
never plan to, so I'm grateful for the correction, Steven.

>> But the __builtins__ namespace can and does include names for
>> non-built-in objects (e.g. help and exit).
>
> Only when running interactively, and only when site.py runs. If you
> remove or disable site.py, the help and exit functions don't get added.

I'm aware of that, and have even mentioned it at least twice in the past.

>> The important point in this
>> context is that iter is in the builtins module, not that it's a
>> built-in function. There are lots of built-in objects that aren't in
>> builtins.
>
>
> I'm afraid I've lost the context, and don't understand why this is
> important. It's true that not all built-in objects are in builtins, and
> not all objects in builtins are built-in, but other than for pedantic
> correctness, why does this matter?

Denis said:

> "iter" is also the name of a builtin function, like "print"

My point was that the issue with iter is a namespace issue. It doesn't
matter that it's a built-in function like "print". Denis could have
meant that either way, so I thought it important to clarify. Why? A
while back there was a thread on the list confusing "built-in"
functions/methods in the io module and the builtins namespace, and
there was even an erroneous bug report filed on a doc string.

https://mail.python.org/pipermail/tutor/2013-June/096218.html
http://bugs.python.org/issue18249