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* Simplify hash function and add test to show effectiveness of the hash

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function.

* Add a better test for deepcopying.

* Add tests to show the __init__() function works like it does for list
  and tuple.  Add related test.

* Have shallow copies of frozensets return self.  Add related test.

* Have frozenset(f) return f if f is already a frozenset. Add related test.

* Beefed-up some existing tests.
This commit is contained in:
Raymond Hettinger 2003-11-23 02:49:05 +00:00
parent baf0f8f24d
commit 49ba4c39c4
2 changed files with 98 additions and 27 deletions
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40
Objects/setobject.c
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@ -64,6 +64,10 @@ frozenset_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
if (!PyArg_UnpackTuple(args, type->tp_name, 0, 1, &iterable))
return NULL;
if (iterable != NULL && iterable->ob_type == &PyFrozenSet_Type) {
Py_INCREF(iterable);
return iterable;
}
return make_new_set(type, iterable);
}
@ -154,6 +158,16 @@ set_copy(PySetObject *so)
return (PyObject *)newso;
}
static PyObject *
frozenset_copy(PySetObject *so)
{
if (so->ob_type == &PyFrozenSet_Type) {
Py_INCREF(so);
return (PyObject *)so;
}
return set_copy(so);
}
PyDoc_STRVAR(copy_doc, "Return a shallow copy of a set.");
static PyObject *
@ -686,7 +700,7 @@ frozenset_hash(PyObject *self)
{
PyObject *it, *item;
PySetObject *so = (PySetObject *)self;
long hash = 0, x;
long hash = 0;
if (so->hash != -1)
return so->hash;
@ -696,14 +710,12 @@ frozenset_hash(PyObject *self)
return -1;
while ((item = PyIter_Next(it)) != NULL) {
x = PyObject_Hash(item);
/* Applying x*(x+1) breaks-up linear relationships so that
h(1) ^ h(2) will be less likely to coincide with hash(3).
Multiplying by a large prime increases the dispersion
between consecutive hashes. Adding one bit from the
original restores the one bit lost during the multiply
(all the products are even numbers). */
hash ^= (x * (x+1) * 3644798167) | (x&1);
/* Multiplying by a large prime increases the bit dispersion for
closely spaced hash values. The is important because some
use cases have many combinations of a small number of
elements with nearby hashes so that many distinct combinations
collapse to only a handful of distinct hash values. */
hash ^= PyObject_Hash(item) * 3644798167;
Py_DECREF(item);
}
Py_DECREF(it);
@ -1096,17 +1108,17 @@ PyTypeObject PySet_Type = {
static PyMethodDef frozenset_methods[] = {
{"copy", (PyCFunction)set_copy, METH_NOARGS,
{"copy", (PyCFunction)frozenset_copy, METH_NOARGS,
copy_doc},
{"__copy__", (PyCFunction)set_copy, METH_NOARGS,
{"__copy__", (PyCFunction)frozenset_copy, METH_NOARGS,
copy_doc},
{"difference",(PyCFunction)set_difference, METH_O,
{"difference", (PyCFunction)set_difference, METH_O,
difference_doc},
{"intersection",(PyCFunction)set_intersection, METH_O,
intersection_doc},
{"issubset",(PyCFunction)set_issubset, METH_O,
{"issubset", (PyCFunction)set_issubset, METH_O,
issubset_doc},
{"issuperset",(PyCFunction)set_issuperset, METH_O,
{"issuperset", (PyCFunction)set_issuperset, METH_O,
issuperset_doc},
{"__reduce__", (PyCFunction)set_reduce, METH_NOARGS,
reduce_doc},