Implement Record.get()

`Record.get()` allows record objects to better masquerade as dicts.

Fixes: #330.

Author: elprans

asyncpg/protocol/record/recordobj.c

@@ -254,6 +254,55 @@ record_item(ApgRecordObject *o, Py_ssize_t i)
 }
 
 
+/* Lookup a record value by its name.  Return 0 on success, -2 if the
+ * value was not found (with KeyError set), and -1 on all other errors.
+ */
+static int
+record_item_by_name(ApgRecordObject *o, PyObject *item, PyObject **result)
+{
+    PyObject *mapped;
+    PyObject *val;
+    Py_ssize_t i;
+
+    mapped = PyObject_GetItem(o->desc->mapping, item);
+    if (mapped == NULL) {
+        goto noitem;
+    }
+
+    if (!PyIndex_Check(mapped)) {
+        Py_DECREF(mapped);
+        goto error;
+    }
+
+    i = PyNumber_AsSsize_t(mapped, PyExc_IndexError);
+    Py_DECREF(mapped);
+
+    if (i < 0) {
+        if (PyErr_Occurred())
+            PyErr_Clear();
+        goto error;
+    }
+
+    val = record_item(o, i);
+    if (val == NULL) {
+        PyErr_Clear();
+        goto error;
+    }
+
+    *result = val;
+
+    return 0;
+
+noitem:
+    _PyErr_SetKeyError(item);
+    return -2;
+
+error:
+    PyErr_SetString(PyExc_RuntimeError, "invalid record descriptor");
+    return -1;
+}
+
+
 static PyObject *
 record_subscript(ApgRecordObject* o, PyObject* item)
 {
@@ -299,42 +348,13 @@ record_subscript(ApgRecordObject* o, PyObject* item)
         }
     }
     else {
-        PyObject *mapped;
-        mapped = PyObject_GetItem(o->desc->mapping, item);
-        if (mapped != NULL) {
-            Py_ssize_t i;
-            PyObject *result;
-
-            if (!PyIndex_Check(mapped)) {
-                Py_DECREF(mapped);
-                goto noitem;
-            }
-
-            i = PyNumber_AsSsize_t(mapped, PyExc_IndexError);
-            Py_DECREF(mapped);
-
-            if (i < 0) {
-                if (PyErr_Occurred()) {
-                    PyErr_Clear();
-                }
-                goto noitem;
-            }
+        PyObject* result;
 
-            result = record_item(o, i);
-            if (result == NULL) {
-                PyErr_Clear();
-                goto noitem;
-            }
+        if (record_item_by_name(o, item, &result) < 0)
+            return NULL;
+        else
             return result;
-        }
-        else {
-            goto noitem;
-        }
     }
-
-noitem:
-    _PyErr_SetKeyError(item);
-    return NULL;
 }
 
 
@@ -483,6 +503,28 @@ record_contains(ApgRecordObject *o, PyObject *arg)
 }
 
 
+static PyObject *
+record_get(ApgRecordObject* o, PyObject* args)
+{
+    PyObject *key;
+    PyObject *defval = Py_None;
+    PyObject *val = NULL;
+    int res;
+
+    if (!PyArg_UnpackTuple(args, "get", 1, 2, &key, &defval))
+        return NULL;
+
+    res = record_item_by_name(o, key, &val);
+    if (res == -2) {
+        PyErr_Clear();
+        Py_INCREF(defval);
+        val = defval;
+    }
+
+    return val;
+}
+
+
 static PySequenceMethods record_as_sequence = {
     (lenfunc)record_length,                          /* sq_length */
     0,                                               /* sq_concat */
@@ -506,6 +548,7 @@ static PyMethodDef record_methods[] = {
     {"values",          (PyCFunction)record_values, METH_NOARGS},
     {"keys",            (PyCFunction)record_keys, METH_NOARGS},
     {"items",           (PyCFunction)record_items, METH_NOARGS},
+    {"get",             (PyCFunction)record_get, METH_VARARGS},
     {NULL,              NULL}           /* sentinel */
 };
 

docs/api/index.rst

@@ -302,6 +302,13 @@ items either by a numeric index or by a field name:
 
       Return an iterator over the *values* of the record *r*.
 
+   .. describe:: get(name[, default])
+
+      Return the value for *name* if the record has a field named *name*,
+      else return *default*. If *default* is not given, return ``None``.
+
+      .. versionadded:: 0.18
+
    .. method:: values()
 
       Return an iterator over the record values.

tests/test_record.py

@@ -49,7 +49,7 @@ def test_record_gc(self):
         mapping = {key: val}
         with self.checkref(key, val):
             r = Record(mapping, (0,))
-            with self.assertRaises(KeyError):
+            with self.assertRaises(RuntimeError):
                 r[key]
             del r
 
@@ -58,7 +58,7 @@ def test_record_gc(self):
         mapping = {key: val}
         with self.checkref(key, val):
             r = Record(mapping, (0,))
-            with self.assertRaises(KeyError):
+            with self.assertRaises(RuntimeError):
                 r[key]
             del r
 
@@ -90,7 +90,7 @@ def test_record_len_getindex(self):
         with self.assertRaisesRegex(KeyError, 'spam'):
             Record(None, (1,))['spam']
 
-        with self.assertRaisesRegex(KeyError, 'spam'):
+        with self.assertRaisesRegex(RuntimeError, 'invalid record descriptor'):
             Record({'spam': 123}, (1,))['spam']
 
     def test_record_slice(self):
@@ -272,6 +272,13 @@ def test_record_cmp(self):
             sorted([r1, r2, r3, r4, r5, r6, r7]),
             [r1, r2, r3, r6, r7, r4, r5])
 
+    def test_record_get(self):
+        r = Record(R_AB, (42, 43))
+        with self.checkref(r):
+            self.assertEqual(r.get('a'), 42)
+            self.assertEqual(r.get('nonexistent'), None)
+            self.assertEqual(r.get('nonexistent', 'default'), 'default')
+
     def test_record_not_pickleable(self):
         r = Record(R_A, (42,))
         with self.assertRaises(Exception):