MySQLdb cursor.execute formatter

Question

I'm working with Python and MySQLdb library. This is part of a code which has been working for a lot of time.

I was testing if the code executes correctly in other Ubuntu versions since we are planning a SO upgrade.

The following code works fine in Ubuntu 12.04 (our baseline system now with Python 2.7.3), Ubuntu 14.04.5 (Python 2.7.6), but doesn't in Ubuntu 16.04.1 (Python 2.7.12):

def updateOutputPath(path):
    try:
        # Connect to database
        with closing(MySQLdb.connect(host=Constants.database_host,
            user=Constants.database_user, passwd=Constants.database_passwd,
            db=Constants.database_name)) as db:

            # Create a cursor to execute queries
            with closing(db.cursor()) as cursor:
                # Execute query
                cursor.execute('UPDATE configuration SET value=%s WHERE ' +
                    'property=\'OUTPUT_PATH\'', (path))
                # Save changes in the database and close connection
                db.commit()
    except MySQLdb.Error, e:
        print_exception('Database error', e)
        print_db_query(cursor)

In the cursor.execute statement, I get the following error: not all arguments converted during string formatting.

Obviously, I checked that the only argument is a valid string describing a valid path, just as when executed in other SO versions.

I could just create a string and pass it to the cursor.execute statement and the problem would be over, but I am curious about this problem.

Any idea why?

I also think it could be related to the python-mysqldb library version and not to the Python version. Its version is 1.2.3-1 in Ubuntu 12.04, 1.2.3-2 in Ubuntu 14.04, and 1.3.7-1 in Ubuntu 16.04 (I assume this update is related to the usage of Mysql-server 5.7 in this OS version).

Answer 1

The parameters passed need to be iterables ie list or tuple. So it should be (path,) and not (path)

cursor.execute('UPDATE configuration SET value=%s WHERE ' +
                    'property=\'OUTPUT_PATH\'', (path,))

>>> path = 'hello'
>>> a = (path)
>>> type(a)
<type 'str'>
>>> b = (path,)
>>> type(b)
<type 'tuple'>
>>> for x in a:
...     print(x)
... 
h
e
l
l
o
>>> for x in b:
...     print(x)
... 
hello

If you pass (path ) it would be the string which will be iterated as each character of path string, and not as items of the tuple, the correct tuple format is (path,))