On Thu, May 28, 2020 at 11:57 AM Steven D'Aprano <st...@pearwood.info>
wrote:
> On Wed, May 27, 2020 at 05:03:09AM +1000, Chris Angelico wrote:
>
> > def foo():
> > if False: x = 0
> > # what is x now?
> >
> > There is no *value* in x, yet x has a state.
>
> In Python code, no, it has no state, it's just an unbound name. That's
> literally a name that has nothing bound to it, hence no state.
>
> In the CPython 3 implementation, it has a hidden state: there's a fixed
> array representing the locals, one of those array slots represents x,
> and there is some kind of C-level special state to distinguish between
> "this slot is filled" and "this slot is not filled". But that's purely
> an optimization. Locals can also be backed by a dict, like globals.
>
> That is what happens in Jython, so when you call locals() you get back
> the actual local namespace dict and modifications to the variables
> works. (Unlike in CPython.)
>
Consider this code:
```
x = 1
def foo():
print(x)
x = 2
foo()
```
Here `print(x)` doesn't print '1', it gives `UnboundLocalError: local
variable 'x' referenced before assignment`. It knows that `x` is meant to
be a local and ignores the global value. That doesn't look like an
implementation detail to me - does Jython do something different?
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/python-ideas@python.org/message/7JEVW5XWZALBJLKHXDW4K2FMVQAQ77J3/
Code of Conduct: http://python.org/psf/codeofconduct/
