MySQLdb INSERT data from JSON using Python error

I'm trying to insert data from a JSON to mysql using MySQLdb. The total number of columns are fixed. Each row of data from the JSON string does not always have values for each column.

Here is my sample code:

    vacant_building = 'http://data.cityofchicago.org/resource/7nii-7srd.json?%24where=date_service_request_was_received=%272014-06-02T00:00:00%27'
    obj = urllib2.urlopen(vacant_building)
    data = json.load(obj)

def insert_mysql(columns, placeholders, data):
    sql = "INSERT INTO vacant_buildings (%s) VALUES (%s)" % (columns, placeholders)
    db = MySQLdb.connect(host="localhost", user="xxxx", passwd="xxxx", db="chicago_data")
    cur = db.cursor()
    cur.execute(sql, data)

for row in data:
    placeholders = ', '.join(['%s'] * len(row))
    columns = ', '.join(c[:64] for c in row.keys())
    row_data = ', '.join(str(value) for value in row.values())
    insert_mysql(columns, placeholders, row_data)

I get the following error: query = query % tuple([db.literal(item) for item in args]) TypeError: not all arguments converted during string formatting

I'm pretty sure the error has to do with the way I'm inserting the values. I've tried to change this to:

sql = "INSERT INTO vacant_buildings (%s) VALUES (%s) (%s)" % (columns, placeholders, data) 

but I get a 1064 error. It's because the values are not enclosed by ' '.

Thoughts to fix?