On 02.10.2015 16:26, Eric V. Smith wrote:

bf'{foo}'

Might succeed or fail, depending on what foo returns for __format__. If
foo is 'bar', it succeeds. If it's '\u1234', it fails.

I know a lot of functions that fail when passing the wrong kind of arguments. What's so wrong with it?

But some of the other arguments are making me think bf'' is a bad idea,
so now I'm leaning towards not implementing it.

I see. Do you think of an alternative solution?


I was digging deeper into the matter of binary/byte strings formatting in order to sympathise why {} is not usable for binary protocols. Let's look at this practical example https://blog.tox.chat/2015/09/fuzzing-the-new-groupchats/ I hope the tox protocol fully qualifies as a wireframe protocol. What he's trying to do it is to fuzzing his new groupchat implementation by creating more-or-less random packages and feed them into tox core to see if it breaks.

He conveniently uses this type of syntax to describe the structure of the first header:

Header 1:  [  Packet ID  (1 b)  |  Chat ID hash  (4 b)  | Sender PK (32 b)  |  nonce (24 b)  ]


Interested in writing a fuzzer, I would find the following really helpful as it mirrors the description within his blog post:

header1 = bf'{packet_id}{chat_id}{sender_pk}{nonce}'

# which should be the same as

header1 = b'%b%b%b%b' % (packet_id, chat_id, sender_pk, nonce)

I wouldn't mind specifying the encoding for all non-byte-string arguments.
Why? Because I would be working with bytes anyway, so no formatting (as in format()) would be necessary in the first place. However, I like the syntax for specifying the structure of (byte) strings.


Does this makes sense?


Best,
Sven

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