On Fri, Aug 17, 2018 at 5:32 AM, Chris Barker via Python-ideas
<python-ideas@python.org> wrote:
> hmm -- made me think that generators are doing something different here --
> and indeed they are. If you use regular functions:
>
> In [30]: def local_modifying(loc):
> ...: """
> ...: adds a "fred" key to the dict passed in
> ...: """
> ...: print("locals passed in:", loc)
> ...: loc['fred'] = 5
> ...: print("locals after adding", loc)
> ...:
>
> In [31]: def test_locals():
> ...: """
> ...: a simple local namespace to use
> ...: """
> ...: a = 1
> ...: b = 2
> ...: local_modifying(locals())
> ...: # does "fred" exist?
> ...: print(locals())
> ...: # and we can access it the usual way
> ...: print("fred:", fred)
> ...:
> In [32]: test_locals()
> locals passed in: {'b': 2, 'a': 1}
> locals after adding {'b': 2, 'a': 1, 'fred': 5}
> {'b': 2, 'a': 1, 'fred': 5}
> fred: 5
>
> It seems you CAN modify the locals dict passed in, and the change will show
> up in the enclosing scope.
>
> But it sounds like that is not guaranteed by the language.
I've no idea what interpreter you're using, but it doesn't work for me.
>>> test_locals()
locals passed in: {'a': 1, 'b': 2}
locals after adding {'a': 1, 'b': 2, 'fred': 5}
{'a': 1, 'b': 2, 'fred': 5}
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 11, in test_locals
NameError: name 'fred' is not defined
You've changed a cached dictionary but haven't actually created a local.
ChrisA
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