[Python-ideas] Jump to function as an an alternative to call function

[Jacob Solinsky]

On Thu, 16 Aug 2018, 12:44 Jacob Solinsky, <jacobsolinsky at gmail.com> wrote:

> I wanted the called, jumped to function to change state in the caller.
> From what I tried to do, passing locals() cannot accomplish this. I have
> made it happen in other languages though.
> In the R language, one can do this
>
> foo = function(){
>        localenv = environment()
>        eval(bar, environment = localenv)
>
> The above code captures the environment of the calling function and
> executes the called function as if the calling function's local environment
> was the global environment. bar doesn't have to be a function, it can be
> any valid R expression captured with the expr() function, and everything in
> R is an expression thus allowing for the full usage code blocks. Outside of
> lisp-like languages this feat seems to usually be impossible though.
>
>
> On Thu, 16 Aug 2018, 12:34 Jonathan Fine, <jfine2358 at gmail.com> wrote:
>
>> Hi Chris
>>
>> Steve and you wrote:
>>
>> >> there
>> >> are times where I have really wanted to access the caller's
>> environment,
>> >> not the environment where my function was defined.
>>
>> > what am I missing? can't you get that by passing locals() in to a
>> function?
>>
>> I think this will fail when values are changed. According to
>> https://docs.python.org/3/library/functions.html#locals
>> > The contents of this dictionary should not be modified; changes may not
>> affect the values of local and free variables used by the interpreter.
>>
>> I suspect that Jacob, the original poster, wants to change state, and
>> also to read changed state.  Jacob, could you confirm or correct, that
>> you want the called function to be able to change state in caller (or
>> perhaps even further up the stack).
>>
>> To finish, here's an interactive example of changing the value of
>> locals().
>>
>> >>> def f(a=1): loc = locals(); yield loc; yield a
>> >>> it = f()
>> >>> ctx = next(it)
>> >>> ctx
>> {'a': 1}  ## This surprised me.
>> >>>
>> >>>
>> >>> def f(a=1): loc = locals(); yield locals(); yield a
>> >>> it = f()
>> >>> ctx = next(it)
>> >>> ctx
>> {'a': 1, 'loc': {...}}
>> >>> ctx['a'] = 3
>> >>> ctx['loc']['a'] = 5
>> >>> next(it) ## Is it 1 or 3 or 5?
>> 1  ## The value of 'a' hasn't changed.
>>
>> --
>> Jonathan
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>
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