object.h:  Added PyType_CheckExact macro.

typeobject.c, type_new():

+ Use the new macro.
+ Assert that the arguments have the right types rather than do incomplete
  runtime checks "sometimes".
+ If this isn't the 1-argument flavor() of type, and there aren't 3 args
  total, produce a "types() takes 1 or 3 args" msg before
  PyArg_ParseTupleAndKeywords produces a "takes exactly 3" msg.

+ Change keyword arg name from "x" to "items".  People passing a mapping
  object can stretch their imaginations <wink>.
+ Simplify the docstring text.

+ Squash another potential buffer overrun.
+ Simplify the keyword-arg loop by decrementing the count of keywords
  remaining instead of incrementing Yet Another Variable; also break
  out early if the number of keyword args remaining hits 0.

Since I hit the function's closing curly brace with this patch, that's
enough of this for now <wink>.

we're ensuring that's true during the format parse, get rid of nkwlist.

the format, instead of waiting until after we can overindex it by
mistake.

the va_list until we are sure we have a format string and need to use it;
this avoid premature initialization and having to finalize it several
different places because of error returns.

this routine will report an error now when it didn't before, but, if so,
it's a legitimate error that should never have been suppressed.

dict API everywhere on it instead of sometimes using the slower mapping
API.

The "need" for this was probably removed by an earlier patch that stopped
the loop right before it from passing NULL to a dict lookup routine.
I still haven't convinced myself that the next loop is correct, so am
leaving the next mysterious PyErr_Clear() call in for now.

+ Generally test nkeywords against 0 instead of keywords against NULL
  (saves a little work if an empty keywords dict is passed, and is
  conceptually more on-target regardless).
+ When a call erroneously specifies a keyword argument both by position
  and by keyword name:
    - It was easy to provoke this routine into an internal buffer overrun
      by using a long argument name.  Now uses PyErr_format instead (which
      computes a safe buffer size).
    - Improved the error msg.

+ Got rid of now-redundant dict typecheck.
+ Renamed nkwds to nkwlist.  Now all the "counting" vrbls have names
  related to the things they're counting in an obvious way.

+ Renamed argslen to nargs.
+ Renamed kwlen to nkeywords.  This one was especially confusing because
  kwlen wasn't the length of the kwlist argument, but of the keywords
  argument.

+ Removed now-redundant tuple typecheck.
+ Renamed "tplen" local to "argslen" (it's the length of the "args"
  argument; I suppose "tp" was for "Tim Peters should rename me
  someday <wink>).

introduced this bug just a little while ago, when *adding* internal error
checks).

vgetargskeywords:  Rewrote the section that crawls over the format string.
+ Added block comment so it won't take the next person 15 minutes to
  reverse-engineer what it's doing.
+ Lined up the "else" clauses.
+ Rearranged the ifs in decreasing order of likelihood (for speed).

and raise an error if they're insane.
vgetargskeywords:  the same, except that since this is an internal routine,
just assert that the arguments are sane.

the kwlist vector whenever there was a mix of positional and keyword
arguments, and the number of positional arguments exceeded the length
of the kwlist vector.  If there was just one more positional arg than
keyword, the kwlist-terminating NULL got passed to PyMapping_HasKeyString,
which set an internal error that vgetargskeywords() then squashed (but
it's impossible to say whether it knew it was masking an error).  If
more than one more positional argument, it went on to pass random trash
to PyMapping_HasKeyString, which is why the example at the start
happened to kill the process.

Pure bugfix candidate.

removing useless obfuscation.

was intended to verify that sub-sequences of lengths 1 and 3 raise
ValueError, but was actually testing string lengths).

        - Describe UnpackTuple()
        - Credit __unicode__ to MAL
Use \pep macro everywhere in body text.
   (Listening to "The Great Gate of Kiev" -- appropriately triumphal
    music for this check-in...)

There's still a lot to do, but it's better now.

    to be covered in an overview article like this.

and suggeest that new code that does not require compatibility with older
Python versions subclass dictionary, list, or str.

happy.  (This does not cover everything it complained about, though.)

and functions: we only need to call PyObject_ClearWeakRefs() if the weakref
list is non-NULL.  Since these objects are common but weakrefs are still
unusual, saving the call at deallocation time makes a lot of sense.

Minor cleanups & markup consistency fixes.

PyObject_CallMethodObArgs().

PyObject_CallFunctionObArgs() and PyObject_CallMethodObArgs() have the
advantage that no format strings need to be parsed.  The CallMethod
variant also avoids creating a new string object in order to retrieve
a method from an object as well.

consistent (lack of) vertical space between sections, and remove some of the
unnecessary cruft that was added in (finally we get to *remove* something
that got generated!).

away completely next release, unless someone complains.

Reported by Thomas Heller.