newbie: self.member syntax seems /really/ annoying

Alex Martelli aleax at mac.com
Wed Sep 12 19:05:41 CEST 2007


Chris Mellon <arkanes at gmail.com> wrote:
   ...
> This is terrible and horrible, please don't use it. That said,
> presenting the magic implicit_self context manager!

...which doesn't work in functions -- just try changing your global
code:

>     with implicit_self(t):
>         print a
>         print b
>         a = 40
>         b = a * 2

into a function and a call to it:

    def f():
        with implicit_self(t):
            print a
            print b
            a = 40
            b = a * 2
    f()

...even with different values for the argument to _getframe.  You just
can't "dynamically" add local variables to a function, beyond the set
the compiler has determined are local (and those are exactly the ones
that are *assigned to* in the function's body -- no less, no more --
where "assigned to" includes name-binding statements such as 'def' and
'class' in addition to plain assignment statements, of course).

Making, say, 'a' hiddenly mean 'x.a', within a function, requires a
decorator that suitably rewrites the function's bytecode... (after
which, it WOULD still be terrible and horrible and not to be used, just
as you say, but it might at least _work_;-).  Main problem is, the
decorator needs to know the set of names to be "faked out" in this
terrible and horrible way at the time the 'def' statement executes: it
can't wait until runtime (to dynamically determine what's in var(self))
before it rewrites the bytecode (well, I guess you _could_ arrange a
complicated system to do that, but it _would_ be ridiculously slow).

You could try defeating the fundamental optimization that stands in your
way by adding, say,
    exec 'pass'
inside the function-needing-fakeouts -- but we're getting deeper and
deeper into the mire...;-)


Alex



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