Merge pull request #9805 from behzadnouri/json-seg-fault

BUG: bug in json lib when frame has length zero

Author: shoyer

doc/source/whatsnew/v0.16.1.txt

@@ -61,6 +61,7 @@ Bug Fixes
 ~~~~~~~~~
 
 - Fixed bug (:issue:`9542`) where labels did not appear properly in legend of ``DataFrame.plot()``. Passing ``label=`` args also now works, and series indices are no longer mutated.
+- Bug in json serialization when frame has length zero.(:issue:`9805`)
 
 
 - Bug in ``scatter_matrix`` draws unexpected axis ticklabels (:issue:`5662`)

pandas/io/tests/test_json/test_pandas.py

@@ -321,6 +321,16 @@ def test_frame_to_json_except(self):
         df = DataFrame([1, 2, 3])
         self.assertRaises(ValueError, df.to_json, orient="garbage")
 
+    def test_frame_empty(self):
+        df = DataFrame(columns=['jim', 'joe'])
+        self.assertFalse(df._is_mixed_type)
+        assert_frame_equal(read_json(df.to_json()), df)
+
+        # mixed type
+        df['joe'] = df['joe'].astype('i8')
+        self.assertTrue(df._is_mixed_type)
+        assert_frame_equal(read_json(df.to_json()), df)
+
     def test_v12_compat(self):
         df = DataFrame(
             [[1.56808523,  0.65727391,  1.81021139, -0.17251653],

pandas/src/ujson/python/objToJSON.c

@@ -457,7 +457,7 @@ static void *PyTimeToJSON(JSOBJ _obj, JSONTypeContext *tc, void *outValue, size_
     PyErr_SetString(PyExc_ValueError, "Failed to convert time");
     return NULL;
   }
-  if (PyUnicode_Check(str)) 
+  if (PyUnicode_Check(str))
   {
     tmp = str;
     str = PyUnicode_AsUTF8String(str);
@@ -479,7 +479,7 @@ static int NpyTypeToJSONType(PyObject* obj, JSONTypeContext* tc, int npyType, vo
   {
     PRINTMARK();
     castfunc = PyArray_GetCastFunc(PyArray_DescrFromType(npyType), NPY_DOUBLE);
-    if (!castfunc) 
+    if (!castfunc)
     {
       PyErr_Format (
           PyExc_ValueError,
@@ -501,7 +501,7 @@ static int NpyTypeToJSONType(PyObject* obj, JSONTypeContext* tc, int npyType, vo
   {
     PRINTMARK();
     castfunc = PyArray_GetCastFunc(PyArray_DescrFromType(npyType), NPY_INT64);
-    if (!castfunc) 
+    if (!castfunc)
     {
       PyErr_Format (
           PyExc_ValueError,
@@ -584,7 +584,12 @@ void NpyArr_iterBegin(JSOBJ _obj, JSONTypeContext *tc)
     obj = (PyArrayObject *) _obj;
   }
 
-  if (PyArray_SIZE(obj) > 0)
+  if (PyArray_SIZE(obj) < 0)
+  {
+    PRINTMARK();
+    GET_TC(tc)->iterNext = NpyArr_iterNextNone;
+  }
+  else
   {
     PRINTMARK();
     npyarr = PyObject_Malloc(sizeof(NpyArrContext));
@@ -624,11 +629,6 @@ void NpyArr_iterBegin(JSOBJ _obj, JSONTypeContext *tc)
     npyarr->columnLabels = GET_TC(tc)->columnLabels;
     npyarr->rowLabels = GET_TC(tc)->rowLabels;
   }
-  else
-  {
-    PRINTMARK();
-    GET_TC(tc)->iterNext = NpyArr_iterNextNone;
-  }
 }
 
 void NpyArr_iterEnd(JSOBJ obj, JSONTypeContext *tc)
@@ -1054,8 +1054,11 @@ void PdBlock_iterBegin(JSOBJ _obj, JSONTypeContext *tc)
         npyarr = GET_TC(tc)->npyarr;
 
         // set the dataptr to our desired column and initialise
-        npyarr->dataptr += npyarr->stride * idx;
-        NpyArr_iterNext(obj, tc);
+        if (npyarr != NULL)
+        {
+            npyarr->dataptr += npyarr->stride * idx;
+            NpyArr_iterNext(obj, tc);
+        }
         GET_TC(tc)->itemValue = NULL;
         ((PyObjectEncoder*) tc->encoder)->npyCtxtPassthru = NULL;
 
@@ -2624,7 +2627,7 @@ PyObject* objToJSON(PyObject* self, PyObject *args, PyObject *kwargs)
 
   if (odefHandler != NULL && odefHandler != Py_None)
   {
-    if (!PyCallable_Check(odefHandler)) 
+    if (!PyCallable_Check(odefHandler))
     {
       PyErr_SetString (PyExc_TypeError, "Default handler is not callable");
       return NULL;