d = {222:50, 210:49, 222:51}

i = 0
stroka = ''

for key in sorted(d.keys(), reverse=True):
    #print (key, ':', d[key])
    stroka = stroka + 'position[]=' + str(d[key])
    i = i + 1
    if i != len(d.keys()):
        stroka = stroka + '&'
    #print (stroka)
    #print (i)

print (stroka)