the last call to the step() method of a user function

PyObject_Repr() can removes the current exception. For example, module_repr()
calls PyErr_Clear() if calling loader.module_repr(mod) failed.

small integers (0 or 1 digit)

supports running only selected tests.  Patch by Zachary Ware.

supports running only selected tests.  Patch by Zachary Ware.

Original patch by Zachary Ware.

Original patch by Zachary Ware.

_PyDict_GetItemId() is more efficient: it only builds the Unicode string once.
Identifiers (dictionary keys) are now created at Python initialization, and if
the creation failed, Python does exit with a fatal error.

Before, PyDict_GetItemString() failure was not handled: structseq_new() could
call PyObject_GC_NewVar() with a negative size, and structseq_dealloc() could
also crash.

PyList_Append() (called by PyArena_AddPyObject()) can fail because of a
MemoryError for example.

PyObject_IsSubclass() can fail and raise a new exception!

Type "o" format of Py_BuildValue() is invalid: it must be "O".

It was easy to miss the call to type->tp_init because it was done in a long
conditional expression. Split the long expression in multiple lines to make the
debug step by step easier.

and ignores exceptions raised during the call

Pass the MemoryError exception to the caller, instead of using empty keys.

As PyDict_GetItem(), PyDict_GetItemString() suppresses all errors that may
occur for historical reasons.

notify exceptions raised by the _PyUnicodeWriter API

bytes is NULL on _PyBytes_Resize() failure

Useed context managers for file I/O.
Removed out-of-dated code and misleading comments.

Useed context managers for file I/O.
Removed out-of-dated code and misleading comments.