MvL made this comment in
http://www.mail-archive.com/python-dev@python.org/msg43844.html

I'm copying it here so it doesn't get lost and because I think he makes
a good point that many people would miss (at least I didn't think of it).
-----------------------------------------------

The macros (unfortunately) allowed
to make non-obvious mistakes. Now that they are gone, people need to
really think of what precisely they want to do.

For example, consider

if (PyInt_Check(o)){
  long val = PyInt_AsLong(o);
  // process
} else if (PyLong_Check(o)) {
  long long val = PyLong_AsLongLong(o);
  // check for overflow
  // process
}

With intobject.h, this code would continue to compile, but work
incorrectly, as the second case will never be executed. It would
be better to port this as

#if Py2.x
if (PyInt_Check(o)){
  long val = PyInt_AsLong(o);
  // process
} else
#endif
if (PyLong_Check(o)) {

i.e. eliminating the int case altogether. For another example,

long foo = PyInt_AsLong(Foo);

has a hidden error in 3.x, with intobject: PyLong_AsLong might
overflow, which the 2.x case doesn't.

So eliminating intobject.h likely helps avoiding subtle errors.

Regards,
Martin