[TD-785]Improve the robustness of python connector

src/connector/python/linux/python2/taos/cursor.py

@@ -26,7 +26,7 @@ class TDengineCursor(object):
     """
 
     def __init__(self, connection=None):
-        self._description = None
+        self._description = []
         self._rowcount = -1
         self._connection = None
         self._result = None
@@ -234,7 +234,7 @@ class TDengineCursor(object):
     def _reset_result(self):
         """Reset the result to unused version.
         """
-        self._description = None
+        self._description = []
         self._rowcount = -1
         if self._result is not None:
             CTaosInterface.freeResult(self._result)

src/connector/python/linux/python3/taos/cursor.py

@@ -27,7 +27,7 @@ class TDengineCursor(object):
     """
 
     def __init__(self, connection=None):
-        self._description = None
+        self._description = []
         self._rowcount = -1
         self._connection = None
         self._result = None
@@ -242,7 +242,7 @@ class TDengineCursor(object):
     def _reset_result(self):
         """Reset the result to unused version.
         """
-        self._description = None
+        self._description = []
         self._rowcount = -1
         if self._result is not None:
             CTaosInterface.freeResult(self._result)

src/connector/python/windows/python2/taos/cursor.py

@@ -27,7 +27,7 @@ class TDengineCursor(object):
     """
 
     def __init__(self, connection=None):
-        self._description = None
+        self._description = []
         self._rowcount = -1
         self._connection = None
         self._result = None
@@ -193,7 +193,7 @@ class TDengineCursor(object):
     def _reset_result(self):
         """Reset the result to unused version.
         """
-        self._description = None
+        self._description = []
         self._rowcount = -1
         if self._result is not None:
             CTaosInterface.freeResult(self._result)

src/connector/python/windows/python3/taos/cursor.py

@@ -28,7 +28,7 @@ class TDengineCursor(object):
     """
 
     def __init__(self, connection=None):
-        self._description = None
+        self._description = []
         self._rowcount = -1
         self._connection = None
         self._result = None
@@ -194,7 +194,7 @@ class TDengineCursor(object):
     def _reset_result(self):
         """Reset the result to unused version.
         """
-        self._description = None
+        self._description = []
         self._rowcount = -1
         if self._result is not None:
             CTaosInterface.freeResult(self._result)