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list_ass_slice(): Document the obscure new intent that deleting a slice

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of no more than 8 elements cannot fail.

listpop():  Take advantage of that its calls to list_resize() and
list_ass_slice() can't fail.  This is assert'ed in a debug build now, but
in an icky way.  That is, you can't say:

	assert(some_call() >= 0);

because then some_call() won't occur at all in a release build.  So it
has to be a big pile of #ifdefs on Py_DEBUG (yuck), or the pleasant:

        status = some_call();
        assert(status >= 0);

But in that case, compilers may whine in a release build, because status
appears unused then.  I'm not certain the ugly trick I used here will
convince all compilers to shut up about status (status is always "used" now,
as the first (ignored) clause in a comma expression).
This commit is contained in:
Tim Peters 2004-07-31 21:53:19 +00:00
parent c0cbc8611b
commit 8fc4a91665
1 changed files with 16 additions and 8 deletions
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24
Objects/listobject.c
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@ -519,6 +519,12 @@ list_clear(PyListObject *a)
return 0;
}
/* a[ilow:ihigh] = v if v != NULL.
* del a[ilow:ihigh] if v == NULL.
*
* Special speed gimmick: when v is NULL and ihigh - ilow <= 8, it's
* guaranteed the call cannot fail.
*/
static int
list_ass_slice(PyListObject *a, int ilow, int ihigh, PyObject *v)
{
@ -823,6 +829,7 @@ listpop(PyListObject *self, PyObject *args)
{
int i = -1;
PyObject *v, *arg = NULL;
int status;
if (!PyArg_UnpackTuple(args, "pop", 0, 1, &arg))
return NULL;
@ -845,16 +852,17 @@ listpop(PyListObject *self, PyObject *args)
}
v = self->ob_item[i];
if (i == self->ob_size - 1) {
if (list_resize(self, self->ob_size - 1) == -1)
return NULL;
return v;
status = list_resize(self, self->ob_size - 1);
assert(status >= 0);
return v; /* and v now owns the reference the list had */
}
Py_INCREF(v);
if (list_ass_slice(self, i, i+1, (PyObject *)NULL) != 0) {
Py_DECREF(v);
return NULL;
}
return v;
status = list_ass_slice(self, i, i+1, (PyObject *)NULL);
assert(status >= 0);
/* Use status, so that in a release build compilers don't
* complain about the unused name.
*/
return status, v;
}
/* Reverse a slice of a list in place, from lo up to (exclusive) hi. */