Yes, target['a'] is supposed to be a list.
In your first post, you showed:



 Nil_MSh:

target = {'a': [], 'b': [], 'c': []}
for i in range(800):
                target['a'].append(act['a'])
                target['b'].append(act['b'])
                target['c'].append(act['c'])



This means you initialized target['a'] to be a list, and then, in the loop, appended a tensor to the list at each iteration.  I.e., at the end of the loop, we should have target['a'] = [act['a'],...,act['a']] where act['a'] is a tensor, and target['a'] is now a list of tensors.
When you encountered your error above, I thought something was wrong with act['a'] and we were checking its type, which is supposed to be a tensor.  You were just now checking the type of target['a'], which is supposed to be a list.
In summary, going off my example from above:



 Ada:

a = torch.rand((1,64,32,32))
b = []
for i in range(800):
    b.append(a)

c = torch.stack(b,dim=2)



we should have a is a tensor, b is a list, and c is a tensor.