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[Tutor] beginning to code


On 22/09/2017 13:34, Steve D'Aprano wrote:
> On Fri, 22 Sep 2017 09:24 pm, Marko Rauhamaa wrote:

>> Yes, following my recipe:
>>
>>     def swap(ref_a, ref_b):
>>         a, b = ref_a.get(), ref_b.get()
>>         ref_a.set(b)
>>         ref_b.set(a)
>>
>>     x = 10
>>     y = "Z"
>>     swap(slot_ref(locals(), "x"), slot_ref(locals(), "y"))
>>     print(x, y)             # "Z" and 10
> 
> 
> No, you failed to follow Bart's instructions and answered a different question.

> You have to pass x and y, not strings 'x' and 'y'. The swap procedure needs to
> accept any variable, given as ordinary bare names swap(x, y), not written as
> strings, or by hard-coding x and y as the variables to swap, or by using a
> string and passing it to exec, or any other loophole.

And being able to pass any lvalue expression, not just simple variable 
names. Such as a[i] or x.y, provided the term is mutable.

(To make it work would require a new reference type. And extra versions 
of the byte-codes or whatever is used to evaluate terms such as:

     a, a[i], x.y

that evaluate a reference rather than the value. So LOADFASTREF as well 
as LOADFAST)

-- 
bartc