In isspace, isalpha, isalnum and isdigit, I see code like:

/* Shortcut for single character strings */
if (PyString_GET_SIZE(self) == 1 &&
    isspace(*p))
    return PyBool_FromLong(1);

Is it intentional to not use:

if (PyString_GET_SIZE(self) == 1))
    return PyBool_FromLong(isspace(*p) != 0);

which would be faster when the result is False (but a tad slower when it is True because of the extra comparison).

Also, is there a reason (other than historical) why the macros Py_RETURN_TRUE and Py_RETURN_FALSE are not used instead of their equivalent functions PyBool_FromLong(1) and PyBool_FromLong(0)?

See:
http://hg.python.org/cpython/file/e87364449954/Objects/stringobject.c#l3324