Import web content to csv only if values are different from those of an excel sheet

[io]

Hi, 

i have the following python script that reads json data from a website 
and writes it in a csv file that i will then import to excel. (i have 
just started since a week with py so i'm a noob!) :
-------------------------------------------------------

import json
import urllib
import csv

url = "http://bitcoincharts.com/t/markets.json"
response = urllib.urlopen(url);
data = json.loads(response.read())

f = open("/home/io/markets.csv","wb")
c = csv.writer(f)

# write headers
c.writerow(["Currency","Symbol","Bid", "Ask", "Volume"])

for d in data :
    if d["currency"] <> "SLL":  #esclude la valuta di secondlife SLL
        if d["bid"] is not None and d["ask"] is not None:
            c.writerow([str(d["currency"]),str(d["symbol"]),str(d
["bid"]),str(d["ask"]),str(d["currency_volume"])])
    
------------------------------------------------------

I have an .ods file (libre calc - i'm on linux) where i have in a sheet 
called "exclusions" a list of names (symbol) the i want to exclude during 
the import from web.

I would like to modify my script so that it can parse each row in the 
"exclusion" sheet and if "symbol"  = "parsed row value" then don't write 
it to the csv file ... to loop on all values in the "exclusion" sheet.

I know it's certainly possible but i don't know how to do that.  (if it 
results easier having the exclusion list in a text file it's not a 
problem, i'm not really stuck with librecalc!)

Thanks in advance to any helpful soul!  :-)