Type hints for msgpack

[dineshbvadhia]

Hello. The code snippet below is to serialize/deserialize python objects including numpy arrays using msgpack (in combination with msgpack_numpy):
What is the type hint(s) for the parameter value in the function msgpack_serialize(value) and msgpack_deserialize(value) ?
How to write the type hints for 'a_list' and ['this', 'that', 'other'] in the write function somedb() ?
How to write the type hints for 'an_array' and np.random.random(1280) in the write function somedb() ?
Do the parameters in the somedb() functions need type hints?

This for Python 3.9+. Thank-you

import numpy as np
from msgpack import packb, unpackb
import msgpack_numpy as m
m.patch()

def msgpack_serialize(value):
    return packb(value, default=m.encode)

def msgpack_deserialize(value):
    return unpackb(value, object_hook=m.decode)

with somedb('mydb':str, 'w':str) as db:
    db.write('a_list', msgpack_serialize(['this', 'that', 'other']))
    db.write('an_array', msgpack_serialize(np.random.random(1280)))

with somedb('mydb':str, 'r':str) as db:
    this_list: list
    this_array: npt.ArrayLike
    this_list = msgpack_deserialize(db.read('a_list'))
    this_array = msgpack_deserialize(db.read('an_array'))

[srittau]

I'm not familiar with numpy or msgpack, but I'll try to answer your questions as well as I can.

The value arguments to msgpack_serialize() and msgpack_deserialize() are just passed on to msgpack.packb() and unpackb(), respectively. While msgpack has no type hints, at least unpackb() could probably simply be annotated using bytes: def msgpack_deserialize(value: bytes):. I couldn't find the definition of packb(), so I don't know how to best annotate it.

In the calls to somedb() you are trying to annotate the passed arguments. This doesn't work and is unnecessary. Just pass the value:

with somedb('mydb', 'w') as db:
    ...

As I assume that packb() returns bytes, you could annotate the return type of msgpack_serialize() as bytes as well. unpackb() and consequently msgpack_deserialize() will probably need to return Any (but I might be mistaken). In this case, you can use annotations like this:

with somedb('mydb':str, 'r':str) as db:
    this_list: list = msgpack_deserialize(db.read('a_list'))
    this_array: npt.ArrayLike = msgpack_deserialize(db.read('an_array'))

[dineshbvadhia]

value in unpackb(value: bytes, object_hook=m.decode) can be annotated as bytes .

value in packb(value, default=m.encode) can take the python objects lists, dicts, others and numpy arrays. So, is the annotation value: Any ?

[srittau]

You could annotate it with a union of all accepted types, but I think using Any is the easiest.

[dineshbvadhia]

Using Union will be better as I can add new object annotations in the future. This has been very informative. Thank-you.