解码和编码数据后输出不同（base64）

Question

If i run:

import base64
data = open('1.dat', 'rb').read()
decoded = base64.b64decode(data)
encoded = base64.b64encode(decoded)
data == encoded

I get "False" as result? How to decode/encode to get the original result?

Answer 1

Base64 is not base64 unfortunately. There may be differences in the implementations. Some implementation for example insert line breaks every 76 characters when encoding, some don't.

Answer 2

You have to b64encode() the data before you b64decode() it:

>>> import base64
>>> data = b"qwertzuiop"
>>> encoded = base64.b64encode(data)
>>> decoded = base64.b64decode(encoded)
>>> data == decoded
True

If your input file is already base64, you need to b64decode() it first, not encode. So your code should be this:

import base64
data = open('1.dat', 'rb').read()  # base64 encoded string
decoded = base64.b64decode(data)
encoded = base64.b64encode(decoded)
data == encoded

If you are getting False as a result, your data is Base64 encoded differently than what the base64 module does.

Answer 3

There is some flexibility in the way base64 is encoded, for example the insertion of newlines. There may also be some alternate characters which the base64 module allows you to specify when encoding and decoding. It's up to you to make sure the proper alternate characters are specified, but otherwise it's easy to compare two strings while ignoring any newlines or whitespace:

''.join(data.split()) == ''.join(encoded.split())