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"""

哈希摘要 - 数字签名/指纹 - 单向哈希函数（没有反函数不可逆）

应用领域：

1. 数据库中的用户敏感信息保存成哈希摘要

2. 给数据生成签名验证数据没有被恶意篡改

3. 云存储服务的秒传功能（去重功能）

"""

class StreamHasher():

"""摘要生成器"""

def __init__(self, algorithm='md5', size=4096):

"""初始化方法

@params:

algorithm - 哈希摘要算法

size - 每次读取数据的大小

"""

self.size = size

cls = getattr(__import__('hashlib'), algorithm.lower())

self.hasher = cls()

def digest(self, file_stream):

"""生成十六进制的摘要字符串"""

# data = file_stream.read(self.size)

# while data:

# self.hasher.update(data)

# data = file_stream.read(self.size)

for data in iter(lambda: file_stream.read(self.size), b''):

self.hasher.update(data)

return self.hasher.hexdigest()

def __call__(self, file_stream):

return self.digest(file_stream)

def main():

"""主函数"""

hasher1 = StreamHasher()

hasher2 = StreamHasher('sha1')

hasher3 = StreamHasher('sha256')

with open('Python-3.7.2.tar.xz', 'rb') as file_stream:

print(hasher1.digest(file_stream))

file_stream.seek(0, 0)

print(hasher2.digest(file_stream))

file_stream.seek(0, 0)

print(hasher3(file_stream))

if __name__ == '__main__':

main()