Dropped keywords passthrough in Json adapter

Pass a dumps function instead. Allow customizing by either arg passing or
subclassing.

The basic Json class now raises ImportError on getquoted() if json is not
available, thus allowing using a customized Json subclass even when the json
module is not available.

doc/src/extras.rst

@@ -152,6 +152,7 @@ versions the `simplejson`_ module is be used if available. Note that the last
 .. _simplejson: http://pypi.python.org/pypi/simplejson/
 
 .. autoclass:: Json
+    :members: dumps
 
 .. autofunction:: register_json
 

lib/_json.py

@@ -48,51 +48,83 @@ JSON_OID = 114
 JSONARRAY_OID = 199
 
 class Json(object):
-    """A wrapper to adapt a Python object to :sql:`json` data type.
+    """
+    An `~psycopg2.extensions.ISQLQuote` wrapper to adapt a Python object to
+    :sql:`json` data type.
 
     `!Json` can be used to wrap any object supported by the underlying
-    `!json` module. Raise `!ImportError` if no module is available.
+    `!json` module. `~psycopg2.extensions.ISQLQuote.getquoted()` will raise
+    `!ImportError` if no module is available.
 
-    Any keyword argument will be passed to the underlying
-    :py:func:`json.dumps()` function, allowing extension and customization. ::
+    The basic usage is to wrap `!Json` around the object to be adapted::
 
         curs.execute("insert into mytable (jsondata) values (%s)",
-            (Json({'a': 100}),))
+            [Json({'a': 100})])
+
+    If you want to customize the adaptation from Python to PostgreSQL you can
+    either provide a custom *dumps* function::
+
+        curs.execute("insert into mytable (jsondata) values (%s)",
+            [Json({'a': 100}, dumps=simplejson.dumps)])
+
+    or you can subclass `!Json` overriding the `dumps()` method::
+
+        class MyJson(Json):
+            def dumps(self, obj):
+                return simplejson.dumps(obj)
+
+        curs.execute("insert into mytable (jsondata) values (%s)",
+            [MyJson({'a': 100})])
 
     .. note::
 
-        You can use `~psycopg2.extensions.register_adapter()` to adapt Python
-        dictionaries to JSON::
+        You can use `~psycopg2.extensions.register_adapter()` to adapt any
+        Python dictionary to JSON, either using `!Json` or any subclass or
+        factory creating a compatible adapter::
 
-            psycopg2.extensions.register_adapter(dict,
-                psycopg2.extras.Json)
+            psycopg2.extensions.register_adapter(dict, psycopg2.extras.Json)
 
-        This setting is global though, so it is not compatible with the use of
-        `register_hstore()`. Any other object supported by the `!json` library
-        used by Psycopg can be registered the same way, but this will clobber
-        the default adaptation rule, so be careful to unwanted side effects.
+        This setting is global though, so it is not compatible with similar
+        adapters such as the one registered by `register_hstore()`. Any other
+        object supported by JSON can be registered the same way, but this will
+        clobber the default adaptation rule, so be careful to unwanted side
+        effects.
 
     """
-    def __init__(self, adapted, **kwargs):
+    def __init__(self, adapted, dumps=None):
         self.adapted = adapted
-        self.kwargs = kwargs
+
+        if dumps is not None:
+            self._dumps = dumps
+        elif json is not None:
+            self._dumps = json.dumps
+        else:
+            self._dumps = None
 
     def __conform__(self, proto):
         if proto is ISQLQuote:
             return self
 
+    def dumps(self, obj):
+        """Serialize *obj* in JSON format.
+
+        The default is to call `!json.dumps()` or the *dumps* function
+        provided in the constructor. You can override this method to create a
+        customized JSON wrapper.
+        """
+        dumps = self._dumps
+        if dumps is not None:
+            return dumps(obj)
+        else:
+            raise ImportError(
+                "json module not available: "
+                "you should provide a dumps function")
+
     def getquoted(self):
-        s = json.dumps(self.adapted, **self.kwargs)
+        s = self.dumps(self.adapted)
         return QuotedString(s).getquoted()
 
 
-# clobber the above class if json is not available
-if json is None:
-    class Json(Json):
-        def __init__(self, adapted):
-            raise ImportError("no json module available")
-
-
 def register_json(conn_or_curs=None, globally=False, loads=None,
         oid=None, array_oid=None):
     """Create and register typecasters converting :sql:`json` type to Python objects.

tests/test_types_extras.py

@@ -781,6 +781,16 @@ class AdaptTypeTestCase(unittest.TestCase):
         return oid
 
 
+def skip_if_json_module(f):
+    """Skip a test if no Python json module is available"""
+    def skip_if_json_module_(self):
+        if psycopg2.extras.json is not None:
+            return self.skipTest("json module is available")
+
+        return f(self)
+
+    return skip_if_json_module_
+
 def skip_if_no_json_module(f):
     """Skip a test if no Python json module is available"""
     def skip_if_no_json_module_(self):
@@ -810,12 +820,20 @@ class JsonTestCase(unittest.TestCase):
     def tearDown(self):
         self.conn.close()
 
+    @skip_if_json_module
     def test_module_not_available(self):
-        from psycopg2.extras import json, Json
-        if json is not None:
-            return self.skipTest("json module is available")
+        from psycopg2.extras import Json
+        self.assertRaises(ImportError, Json(None).getquoted)
 
-        self.assertRaises(ImportError, Json, None)
+    @skip_if_json_module
+    def test_customizable_with_module_not_available(self):
+        from psycopg2.extras import Json
+        class MyJson(Json):
+            def dumps(self, obj):
+                assert obj is None
+                return "hi"
+
+        self.assertEqual(MyJson(None).getquoted(), "'hi'")
 
     @skip_if_no_json_module
     def test_adapt(self):
@@ -830,8 +848,7 @@ class JsonTestCase(unittest.TestCase):
                 psycopg2.extensions.QuotedString(json.dumps(obj)).getquoted())
 
     @skip_if_no_json_module
-    def test_adapt_extended(self):
-        """Json passes through kw arguments to dumps"""
+    def test_adapt_dumps(self):
         from psycopg2.extras import json, Json
 
         class DecimalEncoder(json.JSONEncoder):
@@ -842,7 +859,27 @@ class JsonTestCase(unittest.TestCase):
 
         curs = self.conn.cursor()
         obj = Decimal('123.45')
-        self.assertEqual(curs.mogrify("%s", (Json(obj, cls=DecimalEncoder),)),
+        dumps = lambda obj: json.dumps(obj, cls=DecimalEncoder)
+        self.assertEqual(curs.mogrify("%s", (Json(obj, dumps=dumps),)),
+            b("'123.45'"))
+
+    @skip_if_no_json_module
+    def test_adapt_subclass(self):
+        from psycopg2.extras import json, Json
+
+        class DecimalEncoder(json.JSONEncoder):
+            def default(self, obj):
+                if isinstance(obj, Decimal):
+                    return float(obj)
+                return json.JSONEncoder.default(self, obj)
+
+        class MyJson(Json):
+            def dumps(self, obj):
+                return json.dumps(obj, cls=DecimalEncoder)
+
+        curs = self.conn.cursor()
+        obj = Decimal('123.45')
+        self.assertEqual(curs.mogrify("%s", (MyJson(obj),)),
             b("'123.45'"))
 
     @skip_if_no_json_module