On 2018-04-30 03:49, Tim Peters wrote:
[Soni L. <fakedme...@gmail.com>]
That ain't shadow. That is dynamic scoping.
I don't believe either term is technically accurate, but don't really care.
Shadowing is something different:
def f():
a = 42
def g():
print(a)
local a:
a = 43
g()
g()
should print "42" both times, *if it's lexically scoped*.
Why? The `local` statement, despite its name, and casual talk about
it, isn't _intended_ to create a new scope in any technically accurate
sense. I think what it is intended to do has been adequately
explained several times already. The `a` in `a = 42` is intended to
be exactly the same as the `a` in `a = 43`, changing nothing at all
about Python's lexical scoping rules. It is _the_ `a` local to `f`.
If lexical scoping hasn't changed one whit (and it hasn't), the code
_must_ print 43 first. Same as if `local a:` were replaced by `if
True:`. `local` has no effect on a's value until the new "scope"
_ends_, and never any effect at all on a's visibility (a's "scope").
"local" or not, after `a = 43` there is no scope anywhere, neither
lexical nor dynamic, in which `a` is still bound to 42. _The_ value
of `a` is 43 then, `local` or not.
[snip]
I think it should be lexically scoped.
The purpose of 'local' would be to allow you to use a name that _might_
be used elsewhere.
The problem with a dynamic scope is that you might call some global
function from within the local scope, but find that it's "not working
correctly" because you've inadvertently shadowed a name that the
function refers to.
Imagine, in a local scope, that you call a global function that calls
'len', but you've shadowed 'len'...
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