python提供了一个进行hash加密的模块：hashlib
下面主要记录下其中的md5加密方式
>>> import hashlib
>>> m = hashlib.md5()
>>> m.update("Nobody inspects")
>>> m.update(" the spammish repetition")
>>> m.digest()
'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
>>> m.hexdigest()
'bb649c83dd1ea5c9d9dec9a18df0ffe9'
对以上代码的说明：
1.首先从python直接导入hashlib模块
2.调用hashlib里的md5()生成一个md5 hash对象
3.生成hash对象后，就可以用update方法对字符串进行md5加密的更新处理
4.继续调用update方法会在前面加密的基础上更新加密
5.加密后的二进制结果
6.十六进制结果
如果只需对一条字符串进行加密处理，也可以用一条语句的方式：
>>>print hashlib.new("md5", "Nobody inspects the spammish repetition").hexdigest()
'bb649c83dd1ea5c9d9dec9a18df0ffe9'
引用官方文档部分：
The following values are provided as constant attributes of the hash objects returned by the constructors:
hash.digest_size
The size of the resulting hash in bytes.
hash.block_size
The internal block size of the hash algorithm in bytes.
A hash object has the following methods:
hash.update(arg)
Update the hash object with the string arg. Repeated calls are equivalent to a single call with the concatenation of all the arguments: m.update(a); m.update(b) is equivalent to m.update(a+b).
hash.digest()
Return the digest of the strings passed to the update() method so far. This is a string of digest_size bytes which may contain non-ASCII characters, including null bytes.
hash.hexdigest()
Like digest() except the digest is returned as a string of double length, containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.
hash.copy()
Return a copy (“clone”) of the hash object. This can be used to efficiently compute the digests of strings that share a common initial substring.