How to make a variable's late binding crosses the module boundary?

[Jach Feng]

Chris Angelico 在 2022年8月29日 星期一下午1:58:58 [UTC+8] 的信中寫道：
> On Mon, 29 Aug 2022 at 15:54, Jach Feng <jf... at ms4.hinet.net> wrote: 
> > 
> > Richard Damon 在 2022年8月29日 星期一上午10:47:08 [UTC+8] 的信中寫道： 
> > > On 8/27/22 7:42 AM, Mark Bourne wrote: 
> > > > Jach Feng wrote: 
> > > >> I have two files: test.py and test2.py 
> > > >> --test.py-- 
> > > >> x = 2 
> > > >> def foo(): 
> > > >> print(x) 
> > > >> foo() 
> > > >> 
> > > >> x = 3 
> > > >> foo() 
> > > >> 
> > > >> --test2.py-- 
> > > >> from test import * 
> > > >> x = 4 
> > > >> foo() 
> > > >> 
> > > >> ----- 
> > > >> Run test.py under Winows8.1, I get the expected result: 
> > > >> e:\MyDocument>py test.py 
> > > >> 2 
> > > >> 3 
> > > >> 
> > > >> But when run test2.py, the result is not my expected 2,3,4:-( 
> > > >> e:\MyDocument>py test2.py 
> > > >> 2 
> > > >> 3 
> > > >> 3 
> > > >> 
> > > >> What to do? 
> > > > 
> > > > `from test import *` does not link the names in `test2` to those in 
> > > > `test`. It just binds objects bound to names in `test` to the same 
> > > > names in `test2`. A bit like doing: 
> > > > 
> > > > import test 
> > > > x = test.x 
> > > > foo = test.foo 
> > > > del test 
> > > > 
> > > > Subsequently assigning a different object to `x` in one module does 
> > > > not affect the object assigned to `x` in the other module. So `x = 4` 
> > > > in `test2.py` does not affect the object assigned to `x` in `test.py` 
> > > > - that's still `3`. If you want to do that, you need to import `test` 
> > > > and assign to `test.x`, for example: 
> > > > 
> > > > import test 
> > > > test.x = 4 
> > > > test.foo() 
> > > > 
> > > Yes, fundamental issue is that the statement 
> > > 
> > > from x import y 
> > > 
> > > makes a binding in this module to the object CURRECTLY bound to x.y to 
> > > the name y, but if x.y gets rebound, this module does not track the changes. 
> > > 
> > > You can mutate the object x.y and see the changes, but not rebind it. 
> > > 
> > > If you need to see rebindings, you can't use the "from x import y" form, 
> > > or at a minimum do it as: 
> > > 
> > > 
> > > import x 
> > > 
> > > from x import y 
> > > 
> > > then later to get rebindings to x.y do a 
> > > 
> > > y = x.y 
> > > 
> > > to rebind to the current x.y object. 
> > > 
> > > -- 
> > > Richard Damon 
> > Yes, an extra "import x" will solve my problem too! Sometimes I am wondering why "from x import y" hides x? hum...can't figure out the reason:-) 
> >
> "from x import y" doesn't hide x - it just grabs y. Python does what 
> you tell it to. :) 
> 
> ChrisA
But I had heard people say that "from x import y" did import the whole x module into memory, just as "import x" did, not "grabs y" only. Is this correct?

--Jach