Auto assign decorator - eliminates attribute assignment boilerplate in __init__ functions

autoassign.py

from inspect import signature, Parameter
from functools import wraps, partial

def autoassign(func=None, *, expand_kwargs=False):
    
    if not func:
        return partial(autoassign, expand_kwargs=expand_kwargs)
    sig = signature(func)
    @wraps(func)
    def wrapper(*args, **kwargs):
        instance = args[0]
        bound_args = sig.bind(*args, **kwargs)
        bound_args.apply_defaults()
        for i, (key, value) in enumerate(bound_args.arguments.items()):
            if i == 0 or sig.parameters[key].kind == Parameter.POSITIONAL_ONLY:
                continue
            if expand_kwargs and sig.parameters[key].kind == Parameter.VAR_KEYWORD:
                for kwkey, kwvalue in value.items():
                    setattr(instance, kwkey, kwvalue)
                continue
            setattr(instance, key, value)
        return func(*args, **kwargs)
    return wrapper

"""
class A:
    @autoassign
    def __init__(self, a, b, c=3):
        pass
        
a = A(1, 2)
assert a.a == 1 and a.b == 2 and a.c == 3
"""