Hi I often have the need for a generic object to use as the default value for a function parameter, where 'None' is a valid value for the parameter. For example: _sentinel = object() def first(iterable, default=_sentinel): """Return the first element of the iterable, otherwise the default value (if specified). """ for elem in iterable: # thx to rhettinger for optim. return elem if default is _sentinel: raise StopIteration return default Here, 'default' could legally accept None, so I cannot use that as the default value, nor anything else as far as I'm concerned (I don't know what lives in the iterable, so why should I make assumptions?). Sometimes in the past I've create generic objects, declared a class, e.g.: class NoDef: pass def foo(default=NoDef): ... and lately I've even started using the names of builtin functions (it bothers me a little bit though, that I do that). I think Python needs a builtin for this very purpose. I propose 'nodef', a unique object whose sole purpose is to serve as a default value. It should be unique, in the same sense that 'None' is unique. Comments or alternative solutions?