too simple a question : forward declaration? (also, how to make Python segfault!)

[Jeff Epler]

On Wed, May 14, 2003 at 08:39:53AM -0400, Roy Smith wrote:
> Anyway, the way to fix it up is to delay the execution of the call to 
> create the cross-class references until after both classes have been 
> defined.  My first attempt at this was:
> 
> class foo:
>     def __init__ (self):
>         self.name = "My name is foo"
>         self.barReference = bar()
> 
>     def showBar (self):
>         print self.barReference.name
> 
> class bar:
>     def __init__ (self):
>         self.name = "My name is bar"
>         self.fooReference = foo()
> 
>     def showFoo (self):
>         print self.fooReference.name
> 
> f = foo()
> f.showBar()
> 
> which does something I've never managed to do in 6 years of writing 
> Python code -- it crashes the interpreter with a segfault!
> 
> bash-2.05a$ ./circular2.py
> Segmentation fault
> 
> I've been writing C++ code a bunch for the past couple of months.  I get 
> segfaults all the time in C++, but never in Python.  Maybe some of that 
> static typing compiled language type-bondage bad juju rubbed off on me?  
> Nah, a few minutes of head scratching shows that it's nothing more than 
> a plain old infinite recursion that eventually runs out of memory.  I'm 
> surprised I didn't get a MemoryError, but that's a minor point.

Well, in theory Python should show a very long traceback, ending with 
  File "roysmith.py", line 12, in __init__
    self.fooReference = foo()
  File "roysmith.py", line 4, in __init__
    self.barReference = bar()
RuntimeError: maximum recursion depth exceeded

however, if sys.setrecursionlimit() has been called with a value that's
too large, then Python will happily overflow the C stack.  I thought the
value for the recursion limit was supposed to be sane by default, but
maybe not on all systems..

Jeff