[Python-Dev] Challenge about print >> None

Christian Tismer tismer@appliedbiometrics.com
Tue, 12 Sep 2000 19:35:13 +0300

Fredrik Lundh wrote:
> Vladimir wrote:
> > I understand that you want me to think this way. But that's not my
> > intuitive thinking. I would have written your example like this:
> >
> > def func(file=sys.stdout):
> >     print >> file, args
> >
> > This is a clearer, compared to None which is not a file.

This is not clearer.
Instead, it is presetting a parameter
with a mutable object - bad practice!

> Sigh.  You code doesn't work.  Quoting the PEP, from the section
> that discusses why passing None is the same thing as passing no
> file at all:
>     "Note: defaulting the file argument to sys.stdout at compile time
>     is wrong, because it doesn't work right when the caller assigns to
>     sys.stdout and then uses tables() without specifying the file."
> I was sceptical at first, but the more I see of your counter-arguments,
> the more I support Guido here.  As he pointed out, None usually means
> "pretend I didn't pass this argument" in Python.  No difference here.
> +1 on keeping print as it's implemented (None means default).
> -1 on making None behave like a NullFile.


ciao - chris

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