Locals [was Re: unintuitive for-loop behavior]

[Steven D'Aprano]

On Monday 03 October 2016 12:42, Steve D'Aprano wrote:

> Yes the local would have been created, but you wouldn't see it from an
> ordinary lookup of name x. You would need to use
> 
>     locals()['x']
> 
> to see that it exists. For x to return it, you have to convince the compiler
> to use LOAD_FAST bytecode rather than LOAD_whatever.

Sorry, that first sentence is misleading. The question is, can you create local 
variables inside a function using locals()[name]? IronPython and Jython allow 
it; CPython doesn't.

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



-- 
Steven
git gets easier once you get the basic idea that branches are homeomorphic 
endofunctors mapping submanifolds of a Hilbert space.