free variables /cell objects question

[Peter Otten]

gangesmaster wrote:

> why does CPython require to wrap the free variables if
> closure functions by a cell objects?
> why can't it just pass the object itself?
> 
>>>> def f(x):
> ...     def g():
> ...             return x+2
> ...     return g
> ...
>>>> g5 = f(5)
>>>> dis(g5)
>   3           0 LOAD_DEREF               0 (x)
>               3 LOAD_CONST               1 (2)
>               6 BINARY_ADD
>               7 RETURN_VALUE
>>>> dis(f)
>   2           0 LOAD_CLOSURE             0 (x)
>               3 BUILD_TUPLE              1
>               6 LOAD_CONST               1 (<code objec...
>               9 MAKE_CLOSURE             0
>              12 STORE_FAST               1 (g)
> 
>   4          15 LOAD_FAST                1 (g)
>              18 RETURN_VALUE
>>>>
> 
> i don't see why dereferencing is needed. why not just pass
> the object itself to the MAKE_CLOSURE? i.e.
> 
> LOAD_FAST 0    (x)
> LOAD_CONST 1 (the code object)
> MAKE_CLOSURE 0
> 
> what problem does the cell object solve?

If I understand you correctly:

def f(x):
    def g():
        return x + 2
    x = 42
    return g
assert f(0)() == 44

Peter