How to make a variable's late binding crosses the module boundary?
Jach Feng
jfong at ms4.hinet.net
Sun Aug 28 23:51:43 EDT 2022
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:-)
--Jach
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