Python: Iterating through constructor's arguments

Question

I often find myself writing class constructors like this:

class foo:
    def __init__(self, arg1, arg2, arg3):
        self.arg1 = arg1
        self.arg2 = arg2
         


        

Answer 1

Provided answers rely on *vargs and **kargs arguments, which might not be convenient at all if you want to restrict to a specific set of arguments with specific names: you'll have to do all the checking by hand.

Here's a decorator that stores the provided arguments of a method in its bound instance as attributes with their respective names.

import inspect
import functools

def store_args(method):
    """Stores provided method args as instance attributes."""
    argspec = inspect.getargspec(method)
    defaults = dict(zip( argspec.args[-len(argspec.defaults):], argspec.defaults ))
    arg_names = argspec.args[1:]
    @functools.wraps(method)
    def wrapper(*positional_args, **keyword_args):
        self = positional_args[0]
        # Get default arg values
        args = defaults.copy()
        # Add provided arg values
        list(map( args.update, ( zip(arg_names, positional_args[1:]), keyword_args.items() ) ))
        # Store values in instance as attributes
        self.__dict__.update(args)
        return method(*positional_args, **keyword_args)

    return wrapper

You can then use it like this:

class A:
    @store_args
    def __init__(self, a, b, c=3, d=4, e=5):
        pass

a = A(1,2)
print(a.a, a.b, a.c, a.d, a.e)

Result will be 1 2 3 4 5 on Python3.x or (1, 2, 3, 4, 5) on Python2.x