[Python-ideas] Fix that broken callable builtin

[Paul Moore]

On 19 April 2015 at 01:37, Ionel Cristian Mărieș <contact at ionelmc.ro> wrote:

> Sorry, I pasted a patch with changes unrelated to this discussion. This is
> the gist of the proposed change:
>
>  int
>  PyCallable_Check(PyObject *x)
>  {
>      if (x == NULL)
>          return 0;
> -    return x->ob_type->tp_call;
> +    return x->ob_type->tp_call && _PyObject_HasAttrId(x, &PyId___call__);
>  }
>


OK, thanks. I'd say that doesn't need a PEP. But because it makes
callable() a bit slower, and means that it can execute arbitrary Python
code where it doesn't at the moment, for a pretty small gain (a few rare
cases will no longer give a "false positive" result from callable(), but
other false positives could well still exist), I can imagine the change
being rejected based on the benefits not justifying the cost.

Personally, I don't often use callable(). So I don't have a strong opinion.
But when I *do* use it, it's because I want to check if something is
callable *without* calling it - so the fact that callable() doesn't run
arbitrary code is relevant to me. And the motivating use cases (__call__
being a property on the class object) seem pretty obscure - I've never
encountered anything like that in real life. So overall, I'd be -0 on the
change.

Paul
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