Locals [was Re: unintuitive for-loop behavior]

[Chris Angelico]

On Mon, Oct 3, 2016 at 3:09 PM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> But if it did, then just as in the similar situation in IronPython and Jython,
> you would still need to convince the compiler to use LOAD_FAST or equivalent in
> order to see it. Hence:
>
>
> x = y = 'global'
> def example():
>     locals()['x'] = 'local'
>     locals()['y'] = 'local'
>     if False:
>         # convince the compiler to treat y as a local
>         del y
>     print(x)  # => 'global' in everything
>     print(y)  # => 'local' in Jython/IronPython, UnboundLocalError in CPython

Or convince it to use LOAD_NAME. They're Python 2 implementations,
right? Here's CPython at work...

Python 2.7.12+ (default, Sep  1 2016, 20:27:38)
[GCC 6.2.0 20160822] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> x = y = 'global'
>>> def example():
...     locals()['x'] = 'local'
...     locals()['y'] = 'local'
...     if False:
...         exec("")
...     print(x)
...     print(y)
...
>>> example()
local
local

So apparently, locals() mutations CAN affect name lookups. Happens the
same way in Jython, too.

This is quite a rabbit-hole.

ChrisA