diff --git a/python-package/xgboost/core.py b/python-package/xgboost/core.py
index 45b67f189..1cf3f473d 100644
--- a/python-package/xgboost/core.py
+++ b/python-package/xgboost/core.py
@@ -175,7 +175,7 @@ def _check_call(ret):
         return value from API calls
     """
     if ret != 0:
-        raise XGBoostError(_LIB.XGBGetLastError())
+        raise XGBoostError(py_str(_LIB.XGBGetLastError()))
 
 
 def ctypes2numpy(cptr, length, dtype):
@@ -395,10 +395,11 @@ class DMatrix(object):
                           DeprecationWarning)
 
         if isinstance(data, STRING_TYPES):
-            self.handle = ctypes.c_void_p()
+            handle = ctypes.c_void_p()
             _check_call(_LIB.XGDMatrixCreateFromFile(c_str(data),
                                                      ctypes.c_int(silent),
-                                                     ctypes.byref(self.handle)))
+                                                     ctypes.byref(handle)))
+            self.handle = handle
         elif isinstance(data, scipy.sparse.csr_matrix):
             self._init_from_csr(data)
         elif isinstance(data, scipy.sparse.csc_matrix):
@@ -435,14 +436,15 @@ class DMatrix(object):
         """
         if len(csr.indices) != len(csr.data):
             raise ValueError('length mismatch: {} vs {}'.format(len(csr.indices), len(csr.data)))
-        self.handle = ctypes.c_void_p()
+        handle = ctypes.c_void_p()
         _check_call(_LIB.XGDMatrixCreateFromCSREx(c_array(ctypes.c_size_t, csr.indptr),
                                                   c_array(ctypes.c_uint, csr.indices),
                                                   c_array(ctypes.c_float, csr.data),
                                                   ctypes.c_size_t(len(csr.indptr)),
                                                   ctypes.c_size_t(len(csr.data)),
                                                   ctypes.c_size_t(csr.shape[1]),
-                                                  ctypes.byref(self.handle)))
+                                                  ctypes.byref(handle)))
+        self.handle = handle
 
     def _init_from_csc(self, csc):
         """
@@ -450,14 +452,15 @@ class DMatrix(object):
         """
         if len(csc.indices) != len(csc.data):
             raise ValueError('length mismatch: {} vs {}'.format(len(csc.indices), len(csc.data)))
-        self.handle = ctypes.c_void_p()
+        handle = ctypes.c_void_p()
         _check_call(_LIB.XGDMatrixCreateFromCSCEx(c_array(ctypes.c_size_t, csc.indptr),
                                                   c_array(ctypes.c_uint, csc.indices),
                                                   c_array(ctypes.c_float, csc.data),
                                                   ctypes.c_size_t(len(csc.indptr)),
                                                   ctypes.c_size_t(len(csc.data)),
                                                   ctypes.c_size_t(csc.shape[0]),
-                                                  ctypes.byref(self.handle)))
+                                                  ctypes.byref(handle)))
+        self.handle = handle
 
     def _init_from_npy2d(self, mat, missing, nthread):
         """
@@ -477,7 +480,7 @@ class DMatrix(object):
         # we try to avoid data copies if possible (reshape returns a view when possible
         # and we explicitly tell np.array to try and avoid copying)
         data = np.array(mat.reshape(mat.size), copy=False, dtype=np.float32)
-        self.handle = ctypes.c_void_p()
+        handle = ctypes.c_void_p()
         missing = missing if missing is not None else np.nan
         if nthread is None:
             _check_call(_LIB.XGDMatrixCreateFromMat(
@@ -485,15 +488,16 @@ class DMatrix(object):
                 c_bst_ulong(mat.shape[0]),
                 c_bst_ulong(mat.shape[1]),
                 ctypes.c_float(missing),
-                ctypes.byref(self.handle)))
+                ctypes.byref(handle)))
         else:
             _check_call(_LIB.XGDMatrixCreateFromMat_omp(
                 data.ctypes.data_as(ctypes.POINTER(ctypes.c_float)),
                 c_bst_ulong(mat.shape[0]),
                 c_bst_ulong(mat.shape[1]),
                 ctypes.c_float(missing),
-                ctypes.byref(self.handle),
+                ctypes.byref(handle),
                 nthread))
+        self.handle = handle
 
     def _init_from_dt(self, data, nthread):
         """
@@ -517,14 +521,14 @@ class DMatrix(object):
         for icol in range(data.ncols):
             feature_type_strings[icol] = ctypes.c_char_p(data.stypes[icol].name.encode('utf-8'))
 
-        self.handle = ctypes.c_void_p()
-
+        handle = ctypes.c_void_p()
         _check_call(_LIB.XGDMatrixCreateFromDT(
             ptrs, feature_type_strings,
             c_bst_ulong(data.shape[0]),
             c_bst_ulong(data.shape[1]),
-            ctypes.byref(self.handle),
+            ctypes.byref(handle),
             nthread))
+        self.handle = handle
 
     def __del__(self):
         if hasattr(self, "handle") and self.handle is not None:
@@ -646,7 +650,8 @@ class DMatrix(object):
                                               c_bst_ulong(len(data))))
 
     def save_binary(self, fname, silent=True):
-        """Save DMatrix to an XGBoost buffer.
+        """Save DMatrix to an XGBoost buffer.  Saved binary can be later loaded
+        by providing the path to :py:func:`xgboost.DMatrix` as input.
 
         Parameters
         ----------