how to import torch._six.string_classes in torch 2.0

As an AI language model, I do not have access to the specific implementation details of torch 2.0. However, in general, to import torch._six.string_classes in any version of torch, you can simply use the following line of code:

from torch._six import string_classes

Then, you can use the `string_classes` variable to check if a given variable is a string, like this:

if isinstance(my_var, string_classes):
    # do something
else:
    # do something else

Note that using internal modules like `torch._six` is generally discouraged, as they are not part of the public API and may change or be removed in future versions of torch. It is recommended to use the officially documented modules and functions whenever possible.