python2与python3下的base64模块

Python2的编解码

python2中程序数据类型默认为ASCII，所以需要先将数据解码（decode）成为Unicode类型，然后再编码（encode）成为想要转换的数据类型（gbk，utf-8，gb18030，gb2312），然后再解码成为对应的数据类型显示在屏幕上；

Python3的编解码

python3中程序默认数据类型为Unicode，所以直接将数据编码（encode）成为想要转换的数据类型（gbk，utf-8，gb18030，gb2312），然后解码成为对应的数据类型显示在屏幕上。

base64

Base64编码是一种“防君子不防小人”的编码方式。广泛应用于MIME协议，作为电子邮件的传输编码，生成的编码可逆，后一两位可能有“=”，生成的编码都是ascii字符。

因此对于python2来说，编解码相对要容易一些。python3因为要从Unicode转换一下，相对麻烦一些。一切见下例：

• Python2

 def b64encode(s, altchars=None):
     """Encode a string using Base64.

     s is the string to encode.  Optional altchars must be a string of at least
     length 2 (additional characters are ignored) which specifies an
     alternative alphabet for the '+' and '/' characters.  This allows an
     application to e.g. generate url or filesystem safe Base64 strings.

     The encoded string is returned.
     """
     # Strip off the trailing newline
     encoded = binascii.b2a_base64(s)[:-1]
     if altchars is not None:
         return encoded.translate(string.maketrans(b'+/', altchars[:2]))
     return encoded

 def b64decode(s, altchars=None):
     """Decode a Base64 encoded string.

     s is the string to decode.  Optional altchars must be a string of at least
     length 2 (additional characters are ignored) which specifies the
     alternative alphabet used instead of the '+' and '/' characters.

     The decoded string is returned.  A TypeError is raised if s is
     incorrectly padded.  Characters that are neither in the normal base-64
     alphabet nor the alternative alphabet are discarded prior to the padding
     check.
     """
     if altchars is not None:
         s = s.translate(string.maketrans(altchars[:2], '+/'))
     try:
         return binascii.a2b_base64(s)
     except binascii.Error, msg:
         # Transform this exception for consistency
         raise TypeError(msg)

b64decode源码

这里面的s是一个字符串类型的对象。

 import base64

 s = 'Hello, python'
 b = base64.b64encode(s)
 print 'b为：', b

 c = base64.b64decode(b)
 print 'c为：', c

 # output
 b为： SGVsbG8sIHB5dGhvbg==
 c为： Hello, python

• Python3

 def b64encode(s, altchars=None):
     """Encode the bytes-like object s using Base64 and return a bytes object.

     Optional altchars should be a byte string of length 2 which specifies an
     alternative alphabet for the '+' and '/' characters.  This allows an
     application to e.g. generate url or filesystem safe Base64 strings.
     """
     encoded = binascii.b2a_base64(s, newline=False)
     if altchars is not None:
         assert len(altchars) == 2, repr(altchars)
         return encoded.translate(bytes.maketrans(b'+/', altchars))
     return encoded

 def b64decode(s, altchars=None, validate=False):
     """Decode the Base64 encoded bytes-like object or ASCII string s.

     Optional altchars must be a bytes-like object or ASCII string of length 2
     which specifies the alternative alphabet used instead of the '+' and '/'
     characters.

     The result is returned as a bytes object.  A binascii.Error is raised if
     s is incorrectly padded.

     If validate is False (the default), characters that are neither in the
     normal base-64 alphabet nor the alternative alphabet are discarded prior
     to the padding check.  If validate is True, these non-alphabet characters
     in the input result in a binascii.Error.
     """
     s = _bytes_from_decode_data(s)
     if altchars is not None:
         altchars = _bytes_from_decode_data(altchars)
         assert len(altchars) == 2, repr(altchars)
         s = s.translate(bytes.maketrans(altchars, b'+/'))
     if validate and not re.match(b'^[A-Za-z0-9+/]*={0,2}$', s):
         raise binascii.Error('Non-base64 digit found')
     return binascii.a2b_base64(s)

b64decode源码

这里面的s是一个bytes对象，则字符串首先要经过编码encode()。经过b64encode/b64decode之后的返回结果也是bytes对象，所以我们要转换为Unicode对象就要再使用decode()方法去解码。

 import base64

 s = 'Hello, Python!'
 b = base64.b64encode(s.encode('utf-8')).decode('utf-8')
 print(b)

 c = base64.b64decode(b.encode('utf-8')).decode('utf-8')
 print(c)

 # output
 SGVsbG8sIFB5dGhvbiE=
 Hello, Python!