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Date: Mon, 18 Apr 2011 10:45:16 +1100
Subject: Re: Equivalent code to the bool() built-in function
From: Daniel Kluev <dan.kluev@gmail.com>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:3437

On Sun, Apr 17, 2011 at 8:38 AM, Ben Finney <ben+python@benfinney.id.au> wr=
ote:
> It won't look up the *name* =91bool=92, but it will use that object. Any
> boolean expression is going to be calling the built-in =91bool=92 type
> constructor.
>
> So the answer to the OP's question is no: the function isn't equivalent
> to the type, because the OP's =91bool_equivalent=92 function necessarily
> uses the built-in =91bool=92 type, while the reverse is not true.

Actually, as I was curious myself, I've checked sources and found that
`True if x else False` will _not_ call bool(), it calls
PyObject_IsTrue() pretty much directly.
>>> import dis
>>> def bool2(x):
...     return True if x else False
...
>>> dis.dis(bool2)
  2           0 LOAD_FAST                0 (x)
              3 POP_JUMP_IF_FALSE       10
              6 LOAD_GLOBAL              0 (True)
              9 RETURN_VALUE
        >>   10 LOAD_GLOBAL              1 (False)
             13 RETURN_VALUE


        case POP_JUMP_IF_FALSE:
            w =3D POP();
            if (w =3D=3D Py_True) {
                Py_DECREF(w);
                goto fast_next_opcode;
            }
            if (w =3D=3D Py_False) {
                Py_DECREF(w);
                JUMPTO(oparg);
                goto fast_next_opcode;
            }
            err =3D PyObject_IsTrue(w);
            Py_DECREF(w);
            if (err > 0)
                err =3D 0;
            else if (err =3D=3D 0)
                JUMPTO(oparg);
            else
                break;
            continue;

So technically these implementations are equivalent besides the fact
that bool() is type rather than function.

--=20
With best regards,
Daniel Kluev