Python hashlib模块 （主要记录md5加密）

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.