Refactor the instrument decorator to use inspect to find arguments

[rebkwok]

By using the inspect module to identify the bound arguments passed to the function, we don't need to separate arg and kwarg attributes, and we can handle cases different types of function call, where keywords aren't enforced. We can also now handle keywords captured in a **kwargs parameter.

[bloodearnest]

Looks good.

Have left some comments, this is a fun bit of python wrangling!

[bloodearnest]

Nice touch

[bloodearnest]

Can we move this line up into the decorator body? Then its called once at import time, rather than on every func invocation?

[bloodearnest]

Can we extract default parameters in the decorator body at import time into a dict, and then just look them up at call time?

Combined with pulling out the signature in the decorator at import time, we can build the default param dict then too.

If so, this function might be small enough to not bother with, we can just inline it in the loop, as we can just use ChainMap to look up the parameter in a series of dicts:

(Note, this also include removing the need for _set_attributes, as per my other comment)

...
from collections import ChainMap
...


def instrument(...):
    ...

    def span_decorator(func):
        ...
        func_signature = signature(func)
        default_args = {
             k: v.default for k, v in func_signature.parameters.items()
             if v.default != inspect.Parameter.empty,
        }
        bound_args = {}
     
        @wraps(func)
        def wrap_with_span(*args, **kwargs):
            ...
            if func_attributes is not None:
                bound_args = func_signature.bind(*args, **kwargs).arguments
  
            param_lookup = ChainMap(kwargs, bound_args, default_args)
            for k, v in func_attributes.items():
                try:
                    attributes_dict[k] = str(param_lookup[v])
                except ...:
                    ...

            with tracer.start_as_current_span(
                name, record_exception=record_exception, attributes=attribute_dict,
            ):
                return func(*args, **kwargs)

        return wrap_with_span
 

[bloodearnest]

You can pass attributes at span creation, so we could maybe do

with tracer.start_as_current_span(name, record_exception=record_exception, attributes=attributes_dict):

This would remove the need for _set_attributes alltogether?

[rebkwok]

@bloodearnest Have implemented all your suggestions, much cleaner now I think. Thanks!