def urlretrieve(url, filename, chunksize=8192, overwrite=False):
    if not overwrite and os.path.basename(filename) in get_all_files():
        return
    f = file(filename, "wb")
    nbtries = 3
    while nbtries:
        try:
            res = urllib2.urlopen(url)
        except:
            print "had an error opening", url
            nbtries -= 1
            if not nbtries:
                return
            print "Retrying"
        else:
            break
    done = False
    while not done:
        try:
            data = res.read(chunksize)
            if len(data):
                f.write(data)
            else:
                done = True
        except:
            print "We had an error donwloading", url
            print "removing temporary file :("
            os.remove(filename)