[Python-Dev] PyObject_SetAttr - is it the only way types should set attributes?

Skip Montanaro skip@pobox.com (Skip Montanaro)
Wed, 15 Aug 2001 12:37:10 -0500

    >> I'm also curious about the new type-class unification stuff.  Is it
    >> possible to modify a C object via something like a C struct and have
    >> that change be visible as a modified attrbute at the Python level?

    Guido> Can you clarify this question?  I feel I should be qualified to
    Guido> answer this but I don't understand the question...  Maybe an
    Guido> example would help?

I'll try to channel Jeremy.  Even if I fail, I think the problem I describe
is worth noting for PEP 0266.

Suppose I have an extension module that declares a new type containing a
"foo" slot in the C struct for the type.  If I implement a method named
"bar", it's obviously free to modify any of the contents in the struct in
any way it sees fit.  Now, suppose I also have a getattrfunc that will
return the contents of the "foo" slot when asked to.  There needs not be any
setattrfunc or setattrofunc, yet the value in this slot has to be tracked if
it might be accessed by a programmer.

I suspect this is just one more place a C extension programmer can blow a
gaping hole in his foot, but I worry that there's no obvious way to alert
the programmer to such breakage if/when they upgrade to a version of Python
that tracks globals.  Seems like a source of very subtle bugs.