filename  = 'CCL-mbox-short.txt'
line_count = 0
total_confidence = 0
with open(filename, 'r') as f:
    for line in f.readlines():
        if line.startswith('X-DSPAM-Confidence:'):
            float(line.lstrip('X-DSPAM-Confidence:'))
            line_count +=1
            total_confidence + float(line.lstrip('X-DSPAM-Confidence:'))
            print(total_confidence/line_count)