[Python-Dev] 's' vs 'z' format (was: CVS: python/dist/src/Modules readline.c,2.18,2.19)

[Guido van Rossum]

> On Thu, Jul 06, 2000 at 11:55:14AM -0700, Skip Montanaro wrote:
> >...
> > + /* Exported function to load a readline history file */
> > + 
> > + static PyObject *
> > + read_history_file(self, args)
> > + 	PyObject *self;
> > + 	PyObject *args;
> > + {
> > + 	char *s = NULL;
> > + 	if (!PyArg_ParseTuple(args, "|z:read_history_file", &s))
> 
> This allows somebody to pass read_history_file(None). That doesn't feel
> right. I'd suggest using the 's' format code.
> 
> (if they want the default, then pass nothing at all)

Hm, I actually like this style and would recommend it.  There are
often times where it's useful to pass an explicit parameter that says
"use the default".  For example when writing a Python wrapper:

def my_read_hist(file=None):
    ...do-something...
    readline.read_history_file(file)
    ...do-something-else...

With what you propose, you'd have to write

def my_read_hist(file=None):
    ...do-something...
    if file is None:
        readline.read_history_file()
    else:
        readline.read_history_file(file)
    ...do-something-else...

I don't see how forcing users to do that would be considered elegant.

--Guido van Rossum (home page: http://dinsdale.python.org/~guido/)