Globally override built-in print function?

J. Cliff Dyer jcd at sdf.lonestar.org
Fri Apr 16 19:17:25 CEST 2010


On Fri, 2010-04-16 at 09:50 -0700, Dave W. wrote:
> >>>     old_print = __builtins__.print
> >>>     __builtins__.print = printhook
> >>>     yield
> >>>     __builtins__.print = old_print
> >
> >> I'm pretty sure this is semantically equivalent to my original
> >> code, but I gave it a try anyway.
> >
> > Not at all. Declaring "global print" then assigning to "print"
> > simply changes what the module's "print" variable refers to. Other
> > modules are unaffected.  "Global" variables aren't truly global;
> > they are actually local to the module.  You need to replace it in
> > the __builtins__ because that's where everyone else gets it.
> >
> > > FWIW, it doesn't work, either. :-}
> >
> > Right. Lie answered why. I didn't pay attention and thought you
> > were already using Python 3.
> 
> Thanks, Robert and Lie for the considered and informative responses.
> Getting feedback like this from people who really understand
> Python's internals is invaluable.  Sounds like redirecting
> stdout/stderr is the way to go.  (Especially given that they're not
> the 'real' stdout/stderr---that was news to me!)
> 
> [xref "Suppress output to stdout/stderr in InteractiveInterpreter"]

It's good to remember that names in python are just names.  The objects
that have the names "sys.stdout" and "sys.stderr" are the real deal, but
when you assign a file object to them, you are not actually
"redirecting" anything.  You are assigning a name (sys.stdout) to a
different file object.  The old object still points to STDOUT, but
sys.stdout no longer refers to that object as long as your assignment
remains in scope.




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