查詢日誌文件最大值，過濾一些無用

import  os
import  csv

csvfile = file('？？？？.csv','rb')
spamreader = csv.reader(csvfile)
datalist = []
for row in spamreader:
    if row[0] == 'InvoiceID':
        global keylist
        keylist =row
        continue
    elif row[3] == 'Rounding':
        global Rounding
        Rounding = row[18]
        continue
    elif row[3] == 'InvoiceTotal':
        global  InvoiceTotal
        InvoiceTotal = row[18]
        continue
    elif row[3] == 'StatementTotal':
        global StatementTotal
        StatementTotal = row[18]
        continue
    else:
        datalist.append(row[18])
mincost = 0.0000000
for cost in datalist:
    if cost >  mincost:
        mincost = cost
print cost