typeobject.py 文件源码

def extra_ivars(cls, base):
    c_type = c_typeobj(cls)
    c_base = c_typeobj(base)
    t_size = c_type.tp_basicsize
    b_size = c_base.tp_basicsize

    sizeof_pyobj = ctypes.sizeof(ctypes.py_object)

    if c_type.tp_itemsize or c_base.tp_itemsize:
        return t_size != b_size or c_type.tp_itemsize != c_base.tp_itemsize

    if is_heap_type(cls):
        if c_type.tp_weaklistoffset and c_base.tp_weaklistoffset == 0:
            if c_type.tp_weaklistoffset + sizeof_pyobj == t_size:
                t_size -= sizeof_pyobj
        if c_type.tp_dictoffset and c_base.tp_dictoffset == 0:
            if c_type.tp_dictoffset + sizeof_pyobj == t_size:
                t_size -= sizeof_pyobj

    return t_size != b_size