Format decimal.Decimal as full precision strings in .to_json(...)

Author: Tolker-KU

pandas/_libs/src/vendored/ujson/python/objToJSON.c

@@ -373,6 +373,31 @@ static char *PyTimeToJSON(JSOBJ _obj, JSONTypeContext *tc, size_t *outLen) {
   return outValue;
 }
 
+static char *PyDecimalToUTF8Callback(JSOBJ _obj, JSONTypeContext *tc,
+                                     size_t *len) {
+  PyObject *obj = (PyObject *)_obj;
+  PyObject *str = PyObject_Str(obj);
+  if (str == NULL) {
+    *len = 0;
+    if (!PyErr_Occurred()) {
+      PyErr_SetString(PyExc_ValueError, "Failed to convert decimal");
+    }
+    ((JSONObjectEncoder *)tc->encoder)->errorMsg = "";
+    return NULL;
+  }
+  if (PyUnicode_Check(str)) {
+    PyObject *tmp = str;
+    str = PyUnicode_AsUTF8String(str);
+    Py_DECREF(tmp);
+  }
+
+  GET_TC(tc)->newObj = str;
+
+  *len = PyBytes_GET_SIZE(str);
+  char *outValue = PyBytes_AS_STRING(str);
+  return outValue;
+}
+
 //=============================================================================
 // Numpy array iteration functions
 //=============================================================================
@@ -1467,8 +1492,18 @@ static void Object_beginTypeContext(JSOBJ _obj, JSONTypeContext *tc) {
     tc->type = JT_UTF8;
     return;
   } else if (object_is_decimal_type(obj)) {
-    pc->doubleValue = PyFloat_AsDouble(obj);
-    tc->type = JT_DOUBLE;
+    PyObject* is_nan_py = PyObject_RichCompare(obj, obj, Py_NE);
+    if (is_nan_py == NULL) {
+      goto INVALID;
+    }
+    int is_nan = (is_nan_py == Py_True);
+    Py_DECREF(is_nan_py);
+    if (is_nan) {
+      tc->type = JT_NULL;
+      return;
+    }
+    pc->PyTypeToUTF8 = PyDecimalToUTF8Callback;
+    tc->type = JT_UTF8;
     return;
   } else if (PyDateTime_Check(obj) || PyDate_Check(obj)) {
     if (object_is_nat_type(obj)) {