Checking default arguments

[Neil Cerutti]

On 2007-02-02, Igor V. Rafienko <igorr at ifi.uio.no> wrote:
> Hi,
>
> I was wondering whether it was possible to find out which
> parameter value is being used: the default argument or the
> user-supplied one. That is:  
>
> def foo(x, y="bar"):
>     # how to figure out whether the value of y is 
>     # the default argument, or user-supplied?
>
> foo(1, "bar") => user-supplied
> foo(1)        => default
>
> {}.pop seems to be able to make this dictinction.

You can fake it (this may be how dict.pop work) by not providing
defaults, but using positional arguments.

Here's a silly example, which returns a tuple if the user
supplies the second argument, and a list otherwise.

def foo(x, *args):
  if len(args) == 0:
    y_provided = True
    y = "bar"
  else:
    y_provided = False
    y = args[0]
  if y_provided:
    return (x, y)
  else:
    return [x, y]

-- 
Neil Cerutti
Wonderful bargains for men with 16 and 17 necks --sign at clothing store