TypeError: cannot unpack non-iterable NoneType object

You get this error when you perform a multiple assignment to None (which is of NoneType). For instance:

X_train, y_train, X_test, y_test = None

TypeError: cannot unpack non-iterable NoneType object

So if you get this, the error is most likely that the right-hand part of the assignment is not what you expected (it's nothing).

Splitting/breaking multiple assignment to None resolves this issue.

e.g. This DOESN'T work:

test_set_raw, test_set_transformed, train_set_raw, train_set_transformed = None

This DOES work (no error):

test_set_raw = None
test_set_transformed = None
train_set_raw = None
train_set_transformed = None

I think your X_train, y_train, X_test, y_test are defined inside your load_mnist_imagesfunction, and are thus not defined for your load_dataset function.

You should de-indent your 5 lines from X_train = ... to return X_train, ... and your code might work better then.

You get that error because load_dataset() returns None.

run this and you get the same error:

X_train, y_train, X_test, y_test = None