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.
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
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.
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.
calling __import__. This helps make the expected search locations for encoding
modules be more explicit.
One could use an explicit value for __path__ when making the call to __import__
to force the exact location searched for encodings. This would give the most
strict search path possible if one is worried about malicious code being
imported. The unfortunate side-effect of that is that if __path__ was modified
on 'encodings' on purpose in a safe way it would not be picked up in future
__import__ calls.
