[Python-Dev] Python 2.1 PEPs

[Guido van Rossum]

> On Tue, 17 Apr 2001, Guido van Rossum wrote:
> > This is one of the reasons why I didn't want to add this to the 2.1
> > release at such a late point.  I have no easy way to verify that this
> > is always true, and in fact I have no idea what inspect.stack()[1][3]
> > means. :-(
> 
> Would you have preferred to write
> 
>     sys._getframe().f_back.f_code.co_name
> 
> ?  It's the same thing.

Well, that clears up one mystery.  The rest of your explanation of why
this is correct (as opposed to why this works in the two cases you've
tried :-) is still completely opaque to me...

>     # Define the built-in object "help" to provide interactive help.
>     class Helper:
>         def __repr__(self):
>             import inspect
>             if inspect.stack()[1][3] == '?': # not called from a function
>                 self()
>                 return ''
>             return '<Helper instance>'
>         def __call__(self, arg=None):
>             import pydoc
>             pydoc.help(arg)
>     __builtin__.help = Helper()
> 
> Why the strange check involving inspect.stack()?
> inspect.stack()[1][3] is the co_name of the parent frame.
> If we check that the __repr__ is not being requested by a
> function call, everything works perfectly in IDLE as well
> as the plain interpreter, and the helper object is still safe
> to pass around.  Nothing breaks even if you say help(help).

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