Aaron "Castironpi" Brady wrote:
On Sep 28, 4:47 pm, Terry Reedy <[EMAIL PROTECTED]> wrote:
Aaron "Castironpi" Brady wrote:
inner = lambda: n
when inner is actually compiled outside of outer, it is no longer a
closure over outer's 'n' and 'n' will be looked for in globals instead.
outer = lambda n: inner
outer(0)
<function <lambda> at 0x00A01170>
a=outer(0)
b=outer(1)
a()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in <lambda>
NameError: global name 'n' is not defined
Why doesn't 'inner' know it's been used in two different scopes, and
look up 'n' based on the one it's in?
That would be dynamic rather than lexical scoping.
I couldn't find how those apply on the wikipedia website. It says:
"dynamic scoping can be dangerous and almost no modern languages use
it", but it sounded like that was what closures use. Or maybe it was
what 'inner' in Steven's example would use. I'm confused.
As I understand it, partly from postings here years ago...
Lexical: The namespace scope of 'n' in inner is determined by where
inner is located in the code -- where is is compiled. This is Python
(and nearly all modern languages). Even without closures, the global
scope of a function is the module it is defined in.
Dynamic: The namespace scope of 'n' in inner, how it is looked up, is
determined by where inner is called from. This is what you seemed to be
suggesting -- look up 'n' based on the scope it is *used* in.
Even without closures, dynamic scoping would be if the global scope of a
function for each call were the module it is called in.
tjr
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