John Machin wrote:
On Mar 13, 2:41 am, spir <denis.s...@free.fr> wrote:
Le Thu, 12 Mar 2009 11:13:33 -0400,
Kent Johnson <ken...@tds.net> s'exprima ainsi:
Because local name lookup is faster than global name lookup. Local
variables are stored in an array in the stack frame and accessed by
index. Global names are stored in a dict and accessed with dict access
(dict.__getitem__()).
? I thought this was mainly because a name has first to be searched
(unsuccessfully) locally before a global lookup is launched.
No; for locals, the name resolution is done at COMPILE time.
Also, are locals really stored in an array?
Yes. You seem surprised ... the technique of locals (and args) being
referenced at run time by a constant offset from a frame pointer
register has been around for at least 40 years.
How does lookup then proceed? Is it a kind of (name,ref) sequence?
There is no name lookup at run time. The values of locals (and args)
are obtained by simple array access.
Maybe you need a bit more clarification:
def foo():
a = 10
b = 15
c = a + b
d = 'somewhat'
is (sort of) turned to:
def foo():
locals = [None, None, None, None]
locals[0] = 10
locals[1] = 15
locals[2] = locals[0] + locals[1]
locals[3] = 'somewhat'
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