Implement documented ustruct.pack format codes

[byteit101]

Embedded systems often have to pull apart and put together packed binary structures, and ustruct is very helpful here, though there are 4 unimplemented format specifiers: ? (bool), c (byte, fixed), p (byte-string, pascal), x (padding, in CircuitPython).

As the micropython ustruct documentation refers to the python struct document, I had assumed all the format specifiers would work, but this doesn't appear to be the case.

[jimmo]

As the micropython ustruct documentation refers to the python struct document, I had assumed all the format specifiers would work, but this doesn't appear to be the case.

The micropython docs do explicitly list the supported data types.

Although x is missing... see #12059 (comment)

[byteit101]

Where? I don't see it on https://docs.micropython.org/en/v1.8/pyboard/library/ustruct.html

[jimmo]

That'd the docs for a very old version of micropython (v1.8, released in 2017)

Annoyingly the latest/nightly docs are currently offline, but the docs for the most recent release are here:

http://docs.micropython.org/en/v1.20.0/library/struct.html

[jimmo]

See https://github.com/orgs/micropython/discussions/12456#discussioncomment-7018647 about the latest docs being offline.

[byteit101]

Ah, still interesting that the first result for "micropython ustruct unpack" on google is that old

[jimmo]

4 unimplemented format specifiers: ? (bool), c (byte, fixed), p (byte-string, pascal)

Agreed. It would probably be useful to add these.

x (padding, in CircuitPython).

This was actually added a few days ago. (See the PR I linked above)

[byteit101]

I have already implemented ? on my branch, I can make a PR once I implement c and p

[byteit101]

I have finished and created PR #12458