diff --git a/google/cloud/spanner_dbapi/connection.py b/google/cloud/spanner_dbapi/connection.py
index 869586e363..af3afa7da1 100644
--- a/google/cloud/spanner_dbapi/connection.py
+++ b/google/cloud/spanner_dbapi/connection.py
@@ -38,9 +38,8 @@ def _raise_if_closed(self):
             raise InterfaceError("connection is already closed")
 
     def __handle_update_ddl(self, ddl_statements):
-        """
-        Run the list of Data Definition Language (DDL) statements on the underlying
-        database. Each DDL statement MUST NOT contain a semicolon.
+        """Run the list of Data Definition Language (DDL) statements on the
+        underlying database. Each DDL statement MUST NOT contain a semicolon.
         Args:
             ddl_statements: a list of DDL statements, each without a semicolon.
         Returns:
diff --git a/google/cloud/spanner_dbapi/exceptions.py b/google/cloud/spanner_dbapi/exceptions.py
index a4e973b873..d285caad8f 100644
--- a/google/cloud/spanner_dbapi/exceptions.py
+++ b/google/cloud/spanner_dbapi/exceptions.py
@@ -4,42 +4,82 @@
 # license that can be found in the LICENSE file or at
 # https://developers.google.com/open-source/licenses/bsd
 
+"""Spanner DB API exceptions listed in PEP-249."""
+
 
 class Warning(Exception):
+    """Important DB API warning."""
+
     pass
 
 
 class Error(Exception):
+    """The base class for all the DB API exceptions.
+
+    Does not include :class:`Warning`.
+    """
+
     pass
 
 
 class InterfaceError(Error):
+    """Error related to the database interface
+    rather than the database itself.
+    """
+
     pass
 
 
 class DatabaseError(Error):
+    """Error related to the database."""
+
     pass
 
 
 class DataError(DatabaseError):
+    """Error due to problems with the processed data like
+    division by zero, numeric value out of range, etc.
+    """
+
     pass
 
 
 class OperationalError(DatabaseError):
+    """Error related to the database's operation, e.g. an unexpected
+    disconnect, the data source name is not found, a transaction could not
+    be processed, a memory allocation error, etc.
+    """
+
     pass
 
 
 class IntegrityError(DatabaseError):
+    """Error for cases of relational integrity of the database
+    is affected, e.g. a foreign key check fails.
+    """
+
     pass
 
 
 class InternalError(DatabaseError):
+    """Internal database error, e.g. the cursor is not valid
+    anymore, the transaction is out of sync, etc.
+    """
+
     pass
 
 
 class ProgrammingError(DatabaseError):
+    """Programming error, e.g. table not found or already exists, syntax
+    error in the SQL statement, wrong number of parameters specified, etc.
+    """
+
     pass
 
 
 class NotSupportedError(DatabaseError):
+    """Error for case of a method or database API not
+    supported by the database was used.
+    """
+
     pass