Python-style classes in JavaScript

PyClass.js

//because why not?
//please don't actually use this. Please use idiomatic JavaScript classes or a very thin class layer like github.com/jayferd/pjs
/*
Usage:

var Cat = PyClass({
  __init__: function(self, name) {
    self.name = name;
  },
  chase: function(self, prey) {
    console.log(self.name + ' is chasing ' + prey);
  }
});
var HouseCat = PyClass(Cat, {
  chase: function(self) {
    Cat.chase(self, 'yarn');
  }
});
var kitty = HouseCat('Kitty');
kitty.chase();
*/
function PyClass(sup, defs) {
  if (arguments.length === 1) {
    defs = sup;
    sup = PyClass.Object;
  }
  function cons() {
    if (this instanceof cons) return;
    var self = new cons;
    self.__init__.apply(self, arguments);
    return self;
  }
  var proto = cons.prototype = PyClass.Object(sup.prototype);
  for (var methodName in defs) (function(methodName, method) {
    cons[methodName] = method;
    proto[methodName] = function() {
        method.apply(null, [].concat.apply([this], arguments));
    };
  }(methodName, defs[methodName]));
  return cons;
}
PyClass.Object = function(proto) {
  if (proto) {
    var cons = function(){};
    cons.prototype = proto;
    return new cons;
  }
};
PyClass.Object.prototype.__init__ = function(){};