"extending and embedding" tutorial.

sq_ass_slice instead of the sq_slice slot.

it.

We add some new rules that are required for preserving internal
invariants of types.

1.  If type (or a subclass of type) appears in bases, it must appear
    before any non-type bases.  If a non-type base (like a regular
    new-style class) occurred first, it could trick type into
    allocating the new class an __dict__ which must be impossible.

2. There are several checks that are made of bases when creating a
   type.  Those checks are now repeated when assigning to __bases__.
   We also add the restriction that assignment to __bases__ may not
   change the metaclass of the type.

Add new tests for these cases and for a few other oddball errors that
were no previously tested.  Remove a crasher test that was fixed.

Also some internal refactoring:  Extract the code to find the most
derived metaclass of a type and its bases.  It is now needed in two
places.  Rewrite the TypeError checks in test_descr to use doctest.
The tests now clearly show what exception they expect to see.

Note that ast.c still has a mix of tabs and spaces, because it
attempts to use four-space indents for more of the new code.

Reported by Mike Verdone.

are gone.

This duplicates the behavior whening normally printing exceptions.

Fixes bug 1569356, but at the cost of a minor incompatibility in
locals().  Add test that verifies that the class namespace is not
polluted.  Also clarify the behavior in the library docs.

Along the way, cleaned up the dict_to_map and map_to_dict
implementations and added some comments that explain what they do.

 * use %r instead of backticks since backticks are going away in Py3k
 * PyArena_Malloc() already sets PyErr_NoMemory so we don't need to do it again
 * the signature for ast2obj_int incorrectly used a bool, rather than a long

Don't use a fixed temporary name (gdbm).
Don't use our own temp name creation (dbm).
Should be backported to 2.5.

of some of the common builtin types.

Use a bit in tp_flags for each common builtin type.  Check the bit
to determine if any instance is a subclass of these common types.
The check avoids a function call and O(n) search of the base classes.
The check is done in the various Py*_Check macros rather than calling
PyType_IsSubtype().

All the bits are set in tp_flags when the type is declared
in the Objects/*object.c files because PyType_Ready() is not called
for all the types.  Should PyType_Ready() be called for all types?
If so and the change is made, the changes to the Objects/*object.c files
can be reverted (remove setting the tp_flags).  Objects/typeobject.c
would also have to be modified to add conditions
for Py*_CheckExact() in addition to each the PyType_IsSubtype check.

- clean up bogus use of the {datadescni} environment everywhere

I can't think of an easy way to test this behavior.  It only occurs
when the file system default encoding and the interpreter default
encoding are different, such that you can open the file but not decode
its name.