import fdb
con = fdb.connect(
    host='host', database='database',
    user='IAKUZNETSOV', password='111111'
  )
cur = con.cursor()
cur.execute("select DATA from ATTACHMENTS where OID = '6512165313'")
fileToSave= cur.fetchone()[0]
with open('c:\python5.jpg', 'wb') as f:
    f.write(fileToSave)