As discussed on python-dev, added two extractor functions to the
operator module.
This commit is contained in:
Raymond Hettinger
parent
a45517065a
commit
166958b5df
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@ -300,6 +300,39 @@ Example: Build a dictionary that maps the ordinals from \code{0} to
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\end{verbatim}
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The \module{operator} module also defines tools for generalized attribute
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and item lookups. These are useful for making fast field extractors
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as arguments for \function{map()}, \method{list.sort()},
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\method{itertools.groupby()}, or other functions that expect a
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function argument.
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\begin{funcdesc}{attrgetter}{attr}
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Return a callable object that fetches \var{attr} from its operand.
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After, \samp{f=attrgetter('name')}, the call \samp{f(b)} returns
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\samp{b.name}.
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\versionadded{2.4}
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\end{funcdesc}
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\begin{funcdesc}{itemgetter}{item}
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Return a callable object that fetches \var{item} from its operand.
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After, \samp{f=itemgetter(2)}, the call \samp{f(b)} returns
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\samp{b[2]}.
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\versionadded{2.4}
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\end{funcdesc}
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Examples:
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\begin{verbatim}
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>>> from operator import *
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>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
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>>> getcount = itemgetter(1)
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>>> map(getcount, inventory)
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[3, 2, 5, 1]
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>>> list.sorted(inventory, key=getcount)
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[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
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\end{verbatim}
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\subsection{Mapping Operators to Functions \label{operator-map}}
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This table shows how abstract operations correspond to operator
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@ -227,6 +227,45 @@ class OperatorTestCase(unittest.TestCase):
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self.failIf(operator.is_not(a, b))
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self.failUnless(operator.is_not(a,c))
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def test_attrgetter(self):
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class A:
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pass
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a = A()
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a.name = 'arthur'
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f = operator.attrgetter('name')
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self.assertEqual(f(a), 'arthur')
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f = operator.attrgetter('rank')
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self.assertRaises(AttributeError, f, a)
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f = operator.attrgetter(2)
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self.assertRaises(TypeError, f, a)
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self.assertRaises(TypeError, operator.attrgetter)
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self.assertRaises(TypeError, operator.attrgetter, 1, 2)
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def test_itemgetter(self):
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a = 'ABCDE'
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f = operator.itemgetter(2)
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self.assertEqual(f(a), 'C')
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f = operator.itemgetter(10)
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self.assertRaises(IndexError, f, a)
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f = operator.itemgetter('name')
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self.assertRaises(TypeError, f, a)
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self.assertRaises(TypeError, operator.itemgetter)
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self.assertRaises(TypeError, operator.itemgetter, 1, 2)
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d = dict(key='val')
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f = operator.itemgetter('key')
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self.assertEqual(f(d), 'val')
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f = operator.itemgetter('nonkey')
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self.assertRaises(KeyError, f, d)
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# example used in the docs
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inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
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getcount = operator.itemgetter(1)
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self.assertEqual(map(getcount, inventory), [3, 2, 5, 1])
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self.assertEqual(list.sorted(inventory, key=getcount),
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[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)])
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def test_main():
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test_support.run_unittest(OperatorTestCase)
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@ -104,6 +104,11 @@ Core and builtins
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Extension modules
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-----------------
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- The operator module has two new functions, attrgetter() and
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itemgetter() which are useful for creating fast data extractor
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functions for map(), list.sort(), itertools.groupby(), and
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other functions that expect a function argument.
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- socket.SHUT_{RD,WR,RDWR} was added.
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- os.getsid was added.
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@ -252,13 +252,236 @@ spam2(ge,__ge__, "ge(a, b) -- Same as a>=b.")
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};
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/* itemgetter object **********************************************************/
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typedef struct {
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PyObject_HEAD
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PyObject *item;
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} itemgetterobject;
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static PyTypeObject itemgetter_type;
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static PyObject *
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itemgetter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
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{
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itemgetterobject *ig;
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PyObject *item;
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if (!PyArg_UnpackTuple(args, "itemgetter", 1, 1, &item))
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return NULL;
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/* create itemgetterobject structure */
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ig = PyObject_GC_New(itemgetterobject, &itemgetter_type);
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if (ig == NULL)
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return NULL;
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Py_INCREF(item);
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ig->item = item;
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PyObject_GC_Track(ig);
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return (PyObject *)ig;
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}
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static void
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itemgetter_dealloc(itemgetterobject *ig)
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{
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PyObject_GC_UnTrack(ig);
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Py_XDECREF(ig->item);
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PyObject_GC_Del(ig);
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}
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static int
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itemgetter_traverse(itemgetterobject *ig, visitproc visit, void *arg)
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{
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if (ig->item)
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return visit(ig->item, arg);
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return 0;
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}
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static PyObject *
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itemgetter_call(itemgetterobject *ig, PyObject *args, PyObject *kw)
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{
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PyObject * obj;
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if (!PyArg_UnpackTuple(args, "itemgetter", 1, 1, &obj))
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return NULL;
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return PyObject_GetItem(obj, ig->item);
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}
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PyDoc_STRVAR(itemgetter_doc,
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"itemgetter(item) --> itemgetter object\n\
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\n\
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Return a callable object that fetches the given item from its operand.\n\
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After, f=itemgetter(2), the call f(b) returns b[2].");
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static PyTypeObject itemgetter_type = {
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PyObject_HEAD_INIT(NULL)
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0, /* ob_size */
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"itertools.itemgetter", /* tp_name */
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sizeof(itemgetterobject), /* tp_basicsize */
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0, /* tp_itemsize */
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/* methods */
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(destructor)itemgetter_dealloc, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_compare */
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0, /* tp_repr */
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0, /* tp_as_number */
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0, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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(ternaryfunc)itemgetter_call, /* tp_call */
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0, /* tp_str */
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
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itemgetter_doc, /* tp_doc */
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(traverseproc)itemgetter_traverse, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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0, /* tp_iter */
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0, /* tp_iternext */
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0, /* tp_methods */
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0, /* tp_members */
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0, /* tp_getset */
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0, /* tp_base */
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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0, /* tp_dictoffset */
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0, /* tp_init */
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0, /* tp_alloc */
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itemgetter_new, /* tp_new */
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0, /* tp_free */
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};
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/* attrgetter object **********************************************************/
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typedef struct {
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PyObject_HEAD
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PyObject *attr;
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} attrgetterobject;
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static PyTypeObject attrgetter_type;
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static PyObject *
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attrgetter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
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{
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attrgetterobject *ag;
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PyObject *attr;
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if (!PyArg_UnpackTuple(args, "attrgetter", 1, 1, &attr))
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return NULL;
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/* create attrgetterobject structure */
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ag = PyObject_GC_New(attrgetterobject, &attrgetter_type);
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if (ag == NULL)
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return NULL;
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Py_INCREF(attr);
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ag->attr = attr;
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PyObject_GC_Track(ag);
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return (PyObject *)ag;
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}
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static void
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attrgetter_dealloc(attrgetterobject *ag)
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{
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PyObject_GC_UnTrack(ag);
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Py_XDECREF(ag->attr);
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PyObject_GC_Del(ag);
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}
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static int
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attrgetter_traverse(attrgetterobject *ag, visitproc visit, void *arg)
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{
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if (ag->attr)
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return visit(ag->attr, arg);
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return 0;
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}
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static PyObject *
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attrgetter_call(attrgetterobject *ag, PyObject *args, PyObject *kw)
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{
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PyObject * obj;
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if (!PyArg_UnpackTuple(args, "attrgetter", 1, 1, &obj))
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return NULL;
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return PyObject_GetAttr(obj, ag->attr);
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}
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PyDoc_STRVAR(attrgetter_doc,
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"attrgetter(attr) --> attrgetter object\n\
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\n\
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Return a callable object that fetches the given attribute from its operand.\n\
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After, f=attrgetter('name'), the call f(b) returns b.name.");
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static PyTypeObject attrgetter_type = {
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PyObject_HEAD_INIT(NULL)
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0, /* ob_size */
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"itertools.attrgetter", /* tp_name */
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sizeof(attrgetterobject), /* tp_basicsize */
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0, /* tp_itemsize */
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/* methods */
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(destructor)attrgetter_dealloc, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_compare */
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0, /* tp_repr */
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0, /* tp_as_number */
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0, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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(ternaryfunc)attrgetter_call, /* tp_call */
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0, /* tp_str */
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
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attrgetter_doc, /* tp_doc */
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(traverseproc)attrgetter_traverse, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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0, /* tp_iter */
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0, /* tp_iternext */
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0, /* tp_methods */
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0, /* tp_members */
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0, /* tp_getset */
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0, /* tp_base */
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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0, /* tp_dictoffset */
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0, /* tp_init */
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0, /* tp_alloc */
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attrgetter_new, /* tp_new */
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0, /* tp_free */
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};
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/* Initialization function for the module (*must* be called initoperator) */
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PyMODINIT_FUNC
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initoperator(void)
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{
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/* Create the module and add the functions */
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Py_InitModule4("operator", operator_methods, operator_doc,
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PyObject *m;
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/* Create the module and add the functions */
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m = Py_InitModule4("operator", operator_methods, operator_doc,
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(PyObject*)NULL, PYTHON_API_VERSION);
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if (PyType_Ready(&itemgetter_type) < 0)
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return;
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Py_INCREF(&itemgetter_type);
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PyModule_AddObject(m, "itemgetter", (PyObject *)&itemgetter_type);
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if (PyType_Ready(&attrgetter_type) < 0)
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return;
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Py_INCREF(&attrgetter_type);
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PyModule_AddObject(m, "attrgetter", (PyObject *)&attrgetter_type);
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}
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