[TD-6231]<fix>: fix all none error of stmt multibind in python connector (#7482)

src/connector/python/taos/bind.py

@@ -10,7 +10,8 @@ import sys
 _datetime_epoch = datetime.utcfromtimestamp(0)
 
 def _is_not_none(obj):
-    obj != None
+    return obj != None
+
 class TaosBind(ctypes.Structure):
     _fields_ = [
         ("buffer_type", c_int),
@@ -320,6 +321,14 @@ class TaosMultiBind(ctypes.Structure):
 
     def nchar(self, values):
         # type: (list[str]) -> None
+        self.num = len(values)
+        self.buffer_type = FieldType.C_NCHAR
+        is_null = [1 if v == None else 0 for v in values]
+        self.is_null = cast((c_byte * self.num)(*is_null), c_char_p)
+        
+        if sum(is_null) == self.num:
+            self.length = (c_int32 * len(values))(0 * self.num)
+            return
         if sys.version_info < (3, 0):
             _bytes = [bytes(value) if value is not None else None for value in values]
             buffer_length = max(len(b) + 1 for b in _bytes if b is not None)
@@ -347,9 +356,6 @@ class TaosMultiBind(ctypes.Structure):
             )
         self.length = (c_int32 * len(values))(*[len(b) if b is not None else 0 for b in _bytes])
         self.buffer_length = buffer_length
-        self.num = len(values)
-        self.is_null = cast((c_byte * self.num)(*[1 if v == None else 0 for v in values]), c_char_p)
-        self.buffer_type = FieldType.C_NCHAR
 
     def tinyint_unsigned(self, values):
         self.buffer_type = FieldType.C_TINYINT_UNSIGNED

src/connector/python/tests/test-td6231.py

+from taos import *
+
+conn = connect()
+
+dbname = "pytest_taos_stmt_multi"
+conn.execute("drop database if exists %s" % dbname)
+conn.execute("create database if not exists %s" % dbname)
+conn.select_db(dbname)
+
+conn.execute(
+    "create table if not exists log(ts timestamp, bo bool, nil tinyint, \
+        ti tinyint, si smallint, ii int, bi bigint, tu tinyint unsigned, \
+        su smallint unsigned, iu int unsigned, bu bigint unsigned, \
+        ff float, dd double, bb binary(100), nn nchar(100), tt timestamp)",
+)
+
+stmt = conn.statement("insert into log values(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)")
+
+params = new_multi_binds(16)
+params[0].timestamp((1626861392589, 1626861392590, 1626861392591))
+params[1].bool((True, None, False))
+params[2].tinyint([-128, -128, None]) # -128 is tinyint null
+params[3].tinyint([0, 127, None])
+params[4].smallint([3, None, 2])
+params[5].int([3, 4, None])
+params[6].bigint([3, 4, None])
+params[7].tinyint_unsigned([3, 4, None])
+params[8].smallint_unsigned([3, 4, None])
+params[9].int_unsigned([3, 4, None])
+params[10].bigint_unsigned([3, 4, None])
+params[11].float([3, None, 1])
+params[12].double([3, None, 1.2])
+params[13].binary(["abc", "dddafadfadfadfadfa", None])
+# params[14].nchar(["涛思数据", None, "a long string with 中文字符"])
+params[14].nchar([None, None, None])
+params[15].timestamp([None, None, 1626861392591])
+stmt.bind_param_batch(params)
+stmt.execute()
+
+
+result = stmt.use_result()
+assert result.affected_rows == 3
+result.close()
+
+result = conn.query("select * from log")
+for row in result:
+    print(row)
+result.close()
+stmt.close()
+conn.close()