local variable 'servers' referenced before assignment

Question

def websvc(currency):
    db = MySQLdb.connect("localhost", "root", "aqw", "PFE_Project")
    cursor = db.cursor()
    sql =          


        

Answer 1

Your code not able to reach servers initialization and that is why you getting error. Simply move initialization before try..except. Change this way:

def websvc(currency):
    db = MySQLdb.connect("localhost", "root", "aqw", "PFE_Project")
    cursor = db.cursor()
    sql = "SELECT * FROM myform_composantsserveur"
    servers = []

    try:
        cursor.execute(sql)
        results = cursor.fetchall()
        currency_in = currency
        req = urllib2.urlopen('http://rate-exchange.appspot.com/currency?from=USD&to=%s') % (currency_in) 
        req1 = req.read()
        rate = int(req1['rate'])
        # rate = 0.77112893299999996

        for row in results:
            result = {} 
            result['1'] = row[1]
            result['3'] = int(row[2])
            result['4'] = int(row[3])
            result['5'] = int(row[4])
            result['6'] = row[5]
            result['7'] = int(row[6])
            result['8'] = row[7]
            result['9'] = row[8]
            p = rate * calculations_metric (int(row[2]), int(row[3]), int(row[4]), int(row[6]), row[7])
            result['2'] = p
            keys = result.keys()
            keys.sort()
            servers.append(result)

    except:
        print "Error: unable to fetch data"
    db.close()
    return servers

Answer 2

I see the problem now you have edited it to add the missing parts. It's the exception handler.

If you have an error after try and before servers=[] it will jump to the except clause, then see return servers and fail.

You might want to use a list(), instead of using a dict() to emulate a list ...