Fix warn_explicit(): interpret source=None as source=NULL.

Issue #28915: Replace _PyObject_CallMethodId() with
_PyObject_CallMethodIdObjArgs() in various modules when the format string was
only made of "O" formats, PyObject* arguments.

_PyObject_CallMethodIdObjArgs() avoids the creation of a temporary tuple and
doesn't have to parse a format string.

Replace
   _PyObject_CallArg1(func, arg)
with
   PyObject_CallFunctionObjArgs(func, arg, NULL)

Using the _PyObject_CallArg1() macro increases the usage of the C stack, which
was unexpected and unwanted. PyObject_CallFunctionObjArgs() doesn't have this
issue.

Issue #28858: The change b9c9691c72c5 introduced a regression. It seems like
_PyObject_CallArg1() uses more stack memory than
PyObject_CallFunctionObjArgs().

Replace
    PyObject_CallFunction(func, "O", arg)
and
    PyObject_CallFunction(func, "O", arg, NULL)
with
    _PyObject_CallArg1(func, arg)

Replace
    PyObject_CallFunction(func, NULL)
with
    _PyObject_CallNoArg(func)

_PyObject_CallNoArg() and _PyObject_CallArg1() are simpler and don't allocate
memory on the C stack.

* PyObject_CallFunctionObjArgs(func, NULL) => _PyObject_CallNoArg(func)
* PyObject_CallFunctionObjArgs(func, arg, NULL) => _PyObject_CallArg1(func, arg)

PyObject_CallFunctionObjArgs() allocates 40 bytes on the C stack and requires
extra work to "parse" C arguments to build a C array of PyObject*.

_PyObject_CallNoArg() and _PyObject_CallArg1() are simpler and don't allocate
memory on the C stack.

This change is part of the fastcall project. The change on listsort() is
related to the issue #23507.

The latter function is more readable, faster and doesn't raise exceptions.

in places where Py_DECREF was used.

Don't check if the dict key exists before getting the key. Instead get the key
and handle error.

Issue #26592: _warnings.warn_explicit() now tries to import the warnings module
(Python implementation) if the source parameter is set to be able to log the
traceback where the source was allocated.

Issue #26604:

* Add a new optional source parameter to _warnings.warn() and warnings.warn()
* Modify asyncore, asyncio and _pyio modules to set the source parameter when
  logging a ResourceWarning warning

Issue #26567:

* Add a new function PyErr_ResourceWarning() function to pass the destroyed
  object
* Add a source attribute to warnings.WarningMessage
* Add warnings._showwarnmsg() which uses tracemalloc to get the traceback where
  source object was allocated.

Issue #26568: add new  _showwarnmsg() and _formatwarnmsg() functions to the
warnings module.

The C function warn_explicit() now calls warnings._showwarnmsg() with a
warnings.WarningMessage as parameter, instead of calling warnings.showwarning()
with multiple parameters.

_showwarnmsg() calls warnings.showwarning() if warnings.showwarning() was
replaced. Same for _formatwarnmsg(): call warnings.formatwarning() if it was
replaced.

macro Py_SETREF.

by the warnings.warn(stacklevel=) parameter.

The concept of .pyo files no longer exists. Now .pyc files have an
optional `opt-` tag which specifies if any extra optimizations beyond
the peepholer were applied.

Initial patch by Phil Elson.

are used.

Move also _Py_IDENTIFIER() defintions to the top in modified files to remove
identifiers duplicated in the same file.

instead of creating temporary Unicode string objects

Add also more identifiers in pythonrun.c to avoid temporary Unicode string
objets for the interactive interpreter.

After more tests, I now think that it is the safest option.

call a Python function with an exception set

with an exception set

Warnings may be emitted during Python shutdown, like "unclosed file XXX".
During shutdown, globals()['__main__'] may be None.

characters.

finalization.

sys.argv is set to None during Python finalization: add PyList_Check() to avoid
a crash in PyList_Size().

filenames anymore on Windows.

_Py_DisplaySourceLine()

For example, _PyGC_DumpShutdownStats() calls PyErr_WarnExplicitFormat() while
the import machinery does not work anymore, _Py_DisplaySourceLine() fails when
trying to import the io module.

(should fix Windows buildbot failures on test_gc)

And PyUnicode_GetSize() => PyUnicode_GetLength()

http://mail.python.org/pipermail/python-dev/2011-November/114347.html