如何生成一列B中有而A中沒有的IP段？

"""
生成假數據，並寫入csv file.
引用faker生成ipv4的ip

會生成名為 ip_test.csv的文件，預設1000條數據
"""
def generate_fake_ip(number=1000):
# 先造些假數據，並寫入csv file
fake = Factory.create()

with open("ip_test.csv", "wb") as f:
writer = csv.writer(f)

# 寫入100條假數據, 按照ipv4格式
for _ in xrange(number):
writer.writerow([fake.ipv4(network=False), fake.ipv4(network=False)])

"""
讀取csv文件，並比較A, B兩列
假設A,B自身均沒有重複

比較可簡化為 setB - setA

Note: 未return

"""
def what_ever_you_wanna_call_this_function(fileName="ip_test.csv"):

a = set([])
b = set([])

with open(fileName, "rb") as f:
reader = csv.reader(f)
for row in reader:
a.add(row[0])
b.add(row[1])

result = b - a
print result

"""
讀取csv文件，並比較A,B兩列
假設A,B自身有重複，跟位置信息相關

result為 (index, A, B) 形式的tuple 所組成的list

Note: 未return

"""
def still_need_more(fileName="ip_test.csv"):

result = []

with open(fileName, "rb") as f:
reader = csv.reader(f)
for index, row in enumerate(reader):
if row[0] == row[1]:
result.append((index, row[0], row[1]))

print result