jf...@ms4.hinet.net於 2019年2月26日星期二 UTC+8下午4時46分04秒寫道：
> ast於 2019年2月26日星期二 UTC+8上午12時25分40秒寫道：
> > Hello
> >
> > I noticed a quirk difference between classes and functions
> >
> > >>> x=0
> > >>>
> > >>> class Test:
> > x = x+1
> > print(x)
> > x = x+1
> > print(x)
> >
> > 1
> > 2
> > >>> print(x)
> > 0
> >
> > Previous code doesn't generate any errors.
> > x at the right of = in first "x = x+1" line is
> > the global one (x=0), then x becomes local
> >
> > within a function, this is not allowed
> >
> > >>> x = 0
> > >>>
> > >>> def f():
> > x = x+1
> >
> > >>> f()
> > UnboundLocalError: local variable 'x' referenced before assignment
> >
> > Since x is written inside the function, it is considered as a local
> > variable and x in x+1 is undefined so this throw an exception
> >
> > Any comment ?
>
> May I say that the LEGB rule apply to run time, not compile time?
No. The LEGB apply to compile time where only name and scope are involved.
>
> >>> x = 1
> >>> def f():
> ... print(x)
> ... print(locals())
> ...
> >>> f()
> 1
> {}
> >>> def g():
> ... print(x)
> ... x = 2
> ... print(locals())
> ...
> >>> g()
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 2, in g
> UnboundLocalError: local variable 'x' referenced before assignment
> >>> class X:
> ... print(x)
> ... x = 2
> ...
> 1
> >>>
> The print(x) difference between class and function was caused by that one was
> executed and the other was compiled. The LEGB rule must apply to run time to
> make the language dynamic.
At run time, the binding between name and object can be changed. It's the word
"dynamic" comes from.
What happens in class X when print(x) was encountered? I have no idea how the
LEGB involves there yet:-(
--Jach
>
> Any comment:-)?
>
> --Jach
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