BUG: json invoke default handler for unsupported numpy dtypes

doc/source/io.rst

@@ -1501,45 +1501,34 @@ Fallback Behavior
 
 If the JSON serializer cannot handle the container contents directly it will fallback in the following manner:
 
-- if a ``toDict`` method is defined by the unrecognised object then that
-  will be called and its returned ``dict`` will be JSON serialized.
-- if a ``default_handler`` has been passed to ``to_json`` that will
-  be called to convert the object.
-- otherwise an attempt is made to convert the object to a ``dict`` by
-  parsing its contents. However if the object is complex this will often fail
-  with an ``OverflowError``.
+- if the dtype is unsupported (e.g. ``np.complex``) then the ``default_handler``, if provided, will be called
+  for each value, otherwise an exception is raised.
 
-Your best bet when encountering ``OverflowError`` during serialization
-is to specify a ``default_handler``. For example ``timedelta`` can cause
-problems:
+- if an object is unsupported it will attempt the following:
 
-.. ipython:: python
-   :suppress:
 
-   from datetime import timedelta
-   dftd = DataFrame([timedelta(23), timedelta(seconds=5), 42])
+  * check if the object has defined a ``toDict`` method and call it.
+    A ``toDict`` method should return a ``dict`` which will then be JSON serialized.
 
-.. code-block:: ipython
+  * invoke the ``default_handler`` if one was provided.
 
-   In [141]: from datetime import timedelta
+  * convert the object to a ``dict`` by traversing its contents. However this will often fail
+    with an ``OverflowError`` or give unexpected results.
 
-   In [142]: dftd = DataFrame([timedelta(23), timedelta(seconds=5), 42])
+In general the best approach for unsupported objects or dtypes is to provide a ``default_handler``.
+For example:
+
+.. code-block:: python
 
-   In [143]: dftd.to_json()
+  DataFrame([1.0, 2.0, complex(1.0, 2.0)]).to_json()  # raises
 
-   ---------------------------------------------------------------------------
-   OverflowError                             Traceback (most recent call last)
-   OverflowError: Maximum recursion level reached
+  RuntimeError: Unhandled numpy dtype 15
 
-which can be dealt with by specifying a simple ``default_handler``:
+can be dealt with by specifying a simple ``default_handler``:
 
 .. ipython:: python
 
-   dftd.to_json(default_handler=str)
-
-   def my_handler(obj):
-      return obj.total_seconds()
-   dftd.to_json(default_handler=my_handler)
+   DataFrame([1.0, 2.0, complex(1.0, 2.0)]).to_json(default_handler=str)
 
 .. _io.json_reader:
 

doc/source/whatsnew/v0.18.1.txt

@@ -462,6 +462,8 @@ Bug Fixes
 
 - Bug in ``.loc`` with out-of-bounds in a large indexer would raise ``IndexError`` rather than ``KeyError`` (:issue:`12527`)
 - Bug in resampling when using a ``TimedeltaIndex`` and ``.asfreq()``, would previously not include the final fencepost (:issue:`12926`)
+- Bug in ``DataFrame.to_json`` with unsupported `dtype` not passed to default handler (:issue:`12554`).
+
 - Bug in equality testing with a ``Categorical`` in a ``DataFrame`` (:issue:`12564`)
 - Bug in ``GroupBy.first()``, ``.last()`` returns incorrect row when ``TimeGrouper`` is used (:issue:`7453`)
 

pandas/io/tests/json/test_pandas.py

@@ -809,17 +809,48 @@ def test_mixed_timedelta_datetime(self):
 
     def test_default_handler(self):
         value = object()
-        frame = DataFrame({'a': ['a', value]})
-        expected = frame.applymap(str)
+        frame = DataFrame({'a': [7, value]})
+        expected = DataFrame({'a': [7, str(value)]})
         result = pd.read_json(frame.to_json(default_handler=str))
         assert_frame_equal(expected, result, check_index_type=False)
 
+    def test_default_handler_indirect(self):
+        from pandas.io.json import dumps
+
+        def default(obj):
+            if isinstance(obj, complex):
+                return [('mathjs', 'Complex'),
+                        ('re', obj.real),
+                        ('im', obj.imag)]
+            return str(obj)
+        df_list = [9, DataFrame({'a': [1, 'STR', complex(4, -5)],
+                                 'b': [float('nan'), None, 'N/A']},
+                                columns=['a', 'b'])]
+        expected = ('[9,[[1,null],["STR",null],[[["mathjs","Complex"],'
+                    '["re",4.0],["im",-5.0]],"N\\/A"]]]')
+        self.assertEqual(expected, dumps(df_list, default_handler=default,
+                                         orient="values"))
+
+    def test_default_handler_numpy_unsupported_dtype(self):
+        # GH12554 to_json raises 'Unhandled numpy dtype 15'
+        df = DataFrame({'a': [1, 2.3, complex(4, -5)],
+                        'b': [float('nan'), None, complex(1.2, 0)]},
+                       columns=['a', 'b'])
+        expected = ('[["(1+0j)","(nan+0j)"],'
+                    '["(2.3+0j)","(nan+0j)"],'
+                    '["(4-5j)","(1.2+0j)"]]')
+        self.assertEqual(expected, df.to_json(default_handler=str,
+                                              orient="values"))
+
     def test_default_handler_raises(self):
         def my_handler_raises(obj):
             raise TypeError("raisin")
         self.assertRaises(TypeError,
                           DataFrame({'a': [1, 2, object()]}).to_json,
                           default_handler=my_handler_raises)
+        self.assertRaises(TypeError,
+                          DataFrame({'a': [1, 2, complex(4, -5)]}).to_json,
+                          default_handler=my_handler_raises)
 
     def test_categorical(self):
         # GH4377 df.to_json segfaults with non-ndarray blocks

pandas/src/ujson/python/objToJSON.c

@@ -636,10 +636,6 @@ static int NpyTypeToJSONType(PyObject* obj, JSONTypeContext* tc, int npyType, vo
   }
 
   PRINTMARK();
-  PyErr_Format (
-      PyExc_RuntimeError,
-      "Unhandled numpy dtype %d",
-      npyType);
   return JT_INVALID;
 }
 
@@ -791,6 +787,7 @@ int NpyArr_iterNextItem(JSOBJ obj, JSONTypeContext *tc)
     Py_INCREF(obj);
     ((PyObjectEncoder*) tc->encoder)->npyType = PyArray_TYPE(npyarr->array);
     ((PyObjectEncoder*) tc->encoder)->npyValue = npyarr->dataptr;
+    ((PyObjectEncoder*) tc->encoder)->npyCtxtPassthru = npyarr;
   }
   else
   {
@@ -1917,6 +1914,26 @@ char** NpyArr_encodeLabels(PyArrayObject* labels, JSONObjectEncoder* enc, npy_in
     return ret;
 }
 
+void Object_invokeDefaultHandler(PyObject *obj, PyObjectEncoder *enc)
+{
+  PyObject *tmpObj = NULL;
+  PRINTMARK();
+  tmpObj = PyObject_CallFunctionObjArgs(enc->defaultHandler, obj, NULL);
+  if (!PyErr_Occurred())
+  {
+    if (tmpObj == NULL)
+    {
+      PyErr_SetString(PyExc_TypeError, "Failed to execute default handler");
+    }
+    else
+    {
+      encode (tmpObj, (JSONObjectEncoder*) enc, NULL, 0);
+    }
+  }
+  Py_XDECREF(tmpObj);
+  return;
+}
+
 void Object_beginTypeContext (JSOBJ _obj, JSONTypeContext *tc)
 {
   PyObject *obj, *exc, *toDictFunc, *tmpObj, *values;
@@ -1942,6 +1959,24 @@ void Object_beginTypeContext (JSOBJ _obj, JSONTypeContext *tc)
     PRINTMARK();
     tc->prv = &(enc->basicTypeContext);
     tc->type = NpyTypeToJSONType(obj, tc, enc->npyType, enc->npyValue);
+
+    if (tc->type == JT_INVALID)
+    {
+      if(enc->defaultHandler)
+      {
+        enc->npyType = -1;
+        PRINTMARK();
+        Object_invokeDefaultHandler(enc->npyCtxtPassthru->getitem(enc->npyValue, enc->npyCtxtPassthru->array), enc);
+      }
+      else
+      {
+        PyErr_Format (
+            PyExc_RuntimeError,
+            "Unhandled numpy dtype %d",
+            enc->npyType);
+      }
+    }
+    enc->npyCtxtPassthru = NULL;
     enc->npyType = -1;
     return;
   }
@@ -2528,18 +2563,7 @@ void Object_beginTypeContext (JSOBJ _obj, JSONTypeContext *tc)
 
   if (enc->defaultHandler)
   {
-    PRINTMARK();
-    tmpObj = PyObject_CallFunctionObjArgs(enc->defaultHandler, obj, NULL);
-    if (tmpObj == NULL || PyErr_Occurred())
-    {
-      if (!PyErr_Occurred())
-      {
-        PyErr_SetString(PyExc_TypeError, "Failed to execute default handler");
-      }
-      goto INVALID;
-    }
-    encode (tmpObj, (JSONObjectEncoder*) enc, NULL, 0);
-    Py_DECREF(tmpObj);
+    Object_invokeDefaultHandler(obj, enc);
     goto INVALID;
   }