Added cursor.cast() method

The method exposes the typecasters lookup algorithm. Useful to create
recursive typecasters.

doc/src/cursor.rst

@@ -122,20 +122,6 @@ The ``cursor`` class
         values can be retrieved using |fetch*|_ methods.
 
 
-    .. method:: mogrify(operation [, parameters])
-
-        Return a query string after arguments binding. The string returned is
-        exactly the one that would be sent to the database running the
-        `~cursor.execute()` method or similar.
-
-            >>> cur.mogrify("INSERT INTO test (num, data) VALUES (%s, %s)", (42, 'bar'))
-            "INSERT INTO test (num, data) VALUES (42, E'bar')"
-
-        .. extension::
-
-            The `mogrify()` method is a Psycopg extension to the |DBAPI|.
-
-        
     .. method:: executemany(operation, seq_of_parameters)
       
         Prepare a database operation (query or command) and then execute it
@@ -167,6 +153,34 @@ The ``cursor`` class
         does nothing but it is safe to call it.
 
 
+    .. method:: mogrify(operation [, parameters])
+
+        Return a query string after arguments binding. The string returned is
+        exactly the one that would be sent to the database running the
+        `~cursor.execute()` method or similar.
+
+            >>> cur.mogrify("INSERT INTO test (num, data) VALUES (%s, %s)", (42, 'bar'))
+            "INSERT INTO test (num, data) VALUES (42, E'bar')"
+
+        .. extension::
+
+            The `mogrify()` method is a Psycopg extension to the |DBAPI|.
+
+    .. method:: cast(oid, s)
+
+        Convert a value from the PostgreSQL string representation to a Python
+        object.
+
+        Use the most specific of the typecasters registered by
+        `~psycopg2.extensions.register_type()`.
+
+        .. versionadded:: 2.3.3
+
+        .. extension::
+
+            The `cast()` method is a Psycopg extension to the |DBAPI|.
+
+
 
     .. |fetch*| replace:: `!fetch*()`
 

psycopg/cursor.h

@@ -84,6 +84,7 @@ typedef struct {
 } cursorObject;
 
 /* C-callable functions in cursor_int.c and cursor_ext.c */
+HIDDEN PyObject *curs_get_cast(cursorObject *self, PyObject *oid);
 HIDDEN void curs_reset(cursorObject *self);
 
 /* exception-raising macros */

psycopg/cursor_int.c

@@ -32,6 +32,41 @@
 #include "psycopg/psycopg.h"
 #include "psycopg/cursor.h"
 #include "psycopg/pqpath.h"
+#include "psycopg/typecast.h"
+
+/* curs_get_cast - return the type caster for an oid.
+ *
+ * Return the most specific type caster, from cursor to connection to global.
+ * If no type caster is found, return the default one.
+ *
+ * Return a borrowed reference.
+ */
+
+PyObject *
+curs_get_cast(cursorObject *self, PyObject *oid)
+{
+    PyObject *cast;
+
+    /* cursor lookup */
+    if (self->string_types != NULL && self->string_types != Py_None) {
+        cast = PyDict_GetItem(self->string_types, oid);
+        Dprintf("curs_get_cast:        per-cursor dict: %p", cast);
+        if (cast) { return cast; }
+    }
+
+    /* connection lookup */
+    cast = PyDict_GetItem(self->conn->string_types, oid);
+    Dprintf("curs_get_cast:        per-connection dict: %p", cast);
+    if (cast) { return cast; }
+
+    /* global lookup */
+    cast = PyDict_GetItem(psyco_types, oid);
+    Dprintf("curs_get_cast:        global dict: %p", cast);
+    if (cast) { return cast; }
+
+    /* fallback */
+    return psyco_default_cast;
+}
 
 /* curs_reset - reset the cursor to a clean state */
 

psycopg/cursor_type.c

@@ -629,6 +629,29 @@ psyco_curs_mogrify(cursorObject *self, PyObject *args, PyObject *kwargs)
 #endif
 
 
+/* cast method - convert an oid/string into a Python object */
+#define psyco_curs_cast_doc \
+"cast(oid, s) -> value\n\n" \
+"Convert the string s to a Python object according to its oid.\n\n" \
+"Look for a typecaster first in the cursor, then in its connection," \
+"then in the global register. If no suitable typecaster is found," \
+"leave the value as a string."
+
+static PyObject *
+psyco_curs_cast(cursorObject *self, PyObject *args)
+{
+    PyObject *oid;
+    PyObject *s;
+    PyObject *cast;
+
+    if (!PyArg_ParseTuple(args, "OO", &oid, &s))
+        return NULL;
+
+    cast = curs_get_cast(self, oid);
+    return PyObject_CallFunctionObjArgs(cast, s, (PyObject *)self, NULL);
+}
+
+
 /* fetchone method - fetch one row of results */
 
 #define psyco_curs_fetchone_doc \
@@ -1524,6 +1547,8 @@ static struct PyMethodDef cursorObject_methods[] = {
      METH_VARARGS|METH_KEYWORDS, psyco_curs_scroll_doc},
     /* psycopg extensions */
 #ifdef PSYCOPG_EXTENSIONS
+    {"cast", (PyCFunction)psyco_curs_cast,
+     METH_VARARGS, psyco_curs_cast_doc},
     {"mogrify", (PyCFunction)psyco_curs_mogrify,
      METH_VARARGS|METH_KEYWORDS, psyco_curs_mogrify_doc},
     {"copy_from", (PyCFunction)psyco_curs_copy_from,

psycopg/pqpath.c

@@ -958,19 +958,7 @@ _pq_fetch_tuples(cursorObject *curs)
 
         type = PyInt_FromLong(ftype);
         Dprintf("_pq_fetch_tuples: looking for cast %d:", ftype);
-        if (curs->string_types != NULL && curs->string_types != Py_None) {
-            cast = PyDict_GetItem(curs->string_types, type);
-            Dprintf("_pq_fetch_tuples:     per-cursor dict: %p", cast);
-        }
-        if (cast == NULL) {
-            cast = PyDict_GetItem(curs->conn->string_types, type);
-            Dprintf("_pq_fetch_tuples:     per-connection dict: %p", cast);
-        }
-        if (cast == NULL) {
-            cast = PyDict_GetItem(psyco_types, type);
-            Dprintf("_pq_fetch_tuples:     global dict: %p", cast);
-        }
-        if (cast == NULL) cast = psyco_default_cast;
+        cast = curs_get_cast(curs, type);
 
         /* else if we got binary tuples and if we got a field that
            is binary use the default cast

tests/test_cursor.py

@@ -67,6 +67,38 @@ class CursorTests(unittest.TestCase):
         self.assertEqual('SELECT 10.3;',
             cur.mogrify("SELECT %s;", (Decimal("10.3"),)))
 
+    def test_cast(self):
+        curs = self.conn.cursor()
+
+        self.assertEqual(42, curs.cast(20, '42'))
+        self.assertAlmostEqual(3.14, curs.cast(700, '3.14'))
+
+        try:
+            from decimal import Decimal
+        except ImportError:
+            self.assertAlmostEqual(123.45, curs.cast(1700, '123.45'))
+        else:
+            self.assertEqual(Decimal('123.45'), curs.cast(1700, '123.45'))
+
+        from datetime import date
+        self.assertEqual(date(2011,1,2), curs.cast(1082, '2011-01-02'))
+        self.assertEqual("who am i?", curs.cast(705, 'who am i?'))  # unknown
+
+    def test_cast_specificity(self):
+        curs = self.conn.cursor()
+        self.assertEqual("foo", curs.cast(705, 'foo'))
+
+        D = psycopg2.extensions.new_type((705,), "DOUBLING", lambda v, c: v * 2)
+        psycopg2.extensions.register_type(D, self.conn)
+        self.assertEqual("foofoo", curs.cast(705, 'foo'))
+
+        T = psycopg2.extensions.new_type((705,), "TREBLING", lambda v, c: v * 3)
+        psycopg2.extensions.register_type(T, curs)
+        self.assertEqual("foofoofoo", curs.cast(705, 'foo'))
+
+        curs2 = self.conn.cursor()
+        self.assertEqual("foofoo", curs2.cast(705, 'foo'))
+
 
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)