autoinitarg2attr.py

import inspect
import functools


def arg2attr(clsins_init):

    @functools.wraps(clsins_init)
    def initattrs(self, *a, **kw):
        # build default dict from default args, in reverse order due to
        # the definition syntax is designed.
        argspec = inspect.getargspec(clsins_init)
        default_kw = {k: v for k, v in zip(
            reversed(argspec.args),
            reversed(argspec.defaults),
        )}
        # update the default with args, with the explicit self stripped.
        default_kw.update({k: v for k,v in 
            zip(argspec.args[1:], a)})
        # finally update with keyword arguments.
        default_kw.update(kw)
        for k, v in default_kw.iteritems():
            setattr(self, k, v)
        clsins_init(self, *a, **kw)

    return initattrs


class Foo(object):

    @arg2attr
    def __init__(self, keyword, target='foo', counter=42):
        print self.keyword
        print self.target
        print self.counter


foo1 = Foo('asdf')
assert foo1.keyword == 'asdf'
assert foo1.target == 'foo'
assert foo1.counter == 42

foo2 = Foo('hello', counter=0)
assert foo2.keyword == 'hello'
assert foo2.target == 'foo'
assert foo2.counter == 0

foo3 = Foo(counter=123, keyword='abcd')
assert foo3.keyword == 'abcd'
assert foo3.target == 'foo'
assert foo3.counter == 123

foo4 = Foo('a', 'b', 'c')
assert foo4.keyword == 'a'
assert foo4.target == 'b'
assert foo4.counter == 'c'