Equivalent code to the bool() built-in function

Sun Apr 17 19:45:16 EDT 2011

On Sun, Apr 17, 2011 at 8:38 AM, Ben Finney <ben+python at benfinney.id.au> wrote:
> It won't look up the *name* ‘bool’, but it will use that object. Any
> boolean expression is going to be calling the built-in ‘bool’ type
> constructor.
>> So the answer to the OP's question is no: the function isn't equivalent
> to the type, because the OP's ‘bool_equivalent’ function necessarily
> uses the built-in ‘bool’ 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 = POP();
 if (w == Py_True) {
 Py_DECREF(w);
 goto fast_next_opcode;
 }
 if (w == Py_False) {
 Py_DECREF(w);
 JUMPTO(oparg);
 goto fast_next_opcode;
 }
 err = PyObject_IsTrue(w);
 Py_DECREF(w);
 if (err > 0)
 err = 0;
 else if (err == 0)
 JUMPTO(oparg);
 else
 break;
 continue;
So technically these implementations are equivalent besides the fact
that bool() is type rather than function.
-- 
With best regards,
Daniel Kluev