python csv文件打开错误：_csv.Error: line contains NULL byte

#coding:utf-8
importcsv
csvfilename = 'demo.csv'


print u'################获取某一行'with open(csvfilename, 'rb') as csvfile:
    reader =csv.reader(csvfile)
    rows = [row for row inreader]
print rows[0], rows[1], rows[2], rows[3]

print u'################获取某一列'with open(csvfilename,'rb') as csvfile:
    reader =csv.reader(csvfile)
    column0 = [row[0] for row inreader]
with open(csvfilename, 'rb') as csvfile:
    reader =csv.reader(csvfile)
    column1 = [row[2] for row inreader]

printcolumn0, column1
s = [1,2,3]
for i incolumn0:
    printtype(i)
#print u'sum:',sum(column0)
new_column0 =column0.pop(0)
print u'删除的元素为：', new_column0
print u'删除后的列表:', column0
printtype(column0)
for i incolumn0:
    print type(i)

#coding:utf-8
from __future__ importdivision
importcsv
importcodecs
importxlwt
importpandas as pd
#twsfilename = "mem.csv"#134列
twsfilename = "tws.csv"#123列

#读取行
print u'################获取某一行'with codecs.open(twsfilename, 'rb', "utf-16") as csvfile:
    reader =csv.reader(csvfile)
    column1 = [row for row inreader]
    print column1[1][0].split("    ")
    print type(column1[1][0].split("    "))

print u'################获取某一列'with codecs.open(twsfilename, 'rb', "utf-16") as csvfile:
    reader = csv.reader(csvfile, delimiter='')
    reader.next()#向下跳一行 这行可以注释掉  主要为了去掉标题行
    column1 = [row[1] for row inreader]
    printcolumn1
    print "max:",max(column1)
    s =0
    for i incolumn1:
        x =float(i)
        s +=x
    print "sum:",s,"count:",len(column1)
    #round (s / len(column1), 3)
    print "avg",round (s / len(column1), 3)