base64.b64encode(data)

[Random832]

On Mon, Jun 13, 2016, at 01:16, Steven D'Aprano wrote:
> Suppose instead it returned the Unicode string 'AUERFg=='. That's all
> well and good, but what are you going to do with it? You can't
> transmit it over a serial cable, because that almost surely is going
> to expect bytes, so you have to encode it. You can't embed it in an
> email, because that also expects bytes.

Unless you're using a library that expects to receive strings and encode
them itself. Such as, in the example you so helpfully provide, a file
opened in text mode.
 
> You could write it to a file. If the file is opened in binary mode,
> you have to encode the Unicode string to bytes before you can write
> it. If the file is opened in text mode, Python will accept your
> Unicode string and encode it for you, which could introduce non-
> base64 characters into the file. Consider if the file was opened
> using UTF-16:
> 
> \x00A\x00U\x00E\x00R\x00F\x00g\x00=\x00=
> 
> hardly counts as base64 in any meaningful sense.

Why do you say these things like you assume I will agree with them. It
doesn't, in fact, introduce non-base64 characters because base64
characters are *characters*, not *bytes* and UTF-16 (or EBCDIC or
whatever) is a perfectly valid encoding of those *characters*, and the
recipient will, naturally, open that file in text mode in the same
encoding, and receive the same string, which it can then decode as
base64.