MySQLdb return `Decimal` for a `sum` of `INT`

MySQLdb return `Decimal` for a `sum` of `INT`

This is the table definition I use to reproduce the issue:
create table test_sum_type (kind char(1) not null,
                            n tinyint not null);
Test data:
+------+---+                                                                                                                                                                                                   
| kind | n |                                                                                                                                                                                                   
+------+---+                                                                                                                                                                                                   
| A    | 1 |                                                                                                                                                                                                   
| B    | 1 |                                                                                                                                                                                                   
| A    | 2 |                                                                                                                                                                                                   
+------+---+ 
Query using MySQLdb:
In [32]: cur.execute("select kind, sum(n) from test_sum_type group by kind")                                                                                                                                   
Out[32]: 2L                                                                                                                                                                                                    

In [33]: cur.fetchall()                                                                                                                                                                                        
Out[33]: (('A', Decimal('3')), ('B', Decimal('1')))                                                                                                                                                            

In [34]: cur.execute("select kind, n from test_sum_type")                                                                                                                                                      
Out[34]: 3L                                                                                                                                                                                                    

In [35]: cur.fetchall()                                                                                                                                                                                        
Out[35]: (('A', 1), ('B', 1), ('A', 2)) 
As you can see, the resulting column is a Decimal when I use sum.
I've looked into the source code of MySQLdb, there're only two field types set up to be converted to Decimal by default: DECIMAL and NEWDECIMAL.
What may be the reason of this? Is there any way to check the schema of some tempo