How can I update the counter value only once in each run, but share it among all the methods in the class in nengo?

General Discussion
2

I believe the solution I proposed in your other thread (i.e., using multi-dimensional outputs for nodes) will solve this issue.

However, if you really want to use the approach you’ve taken above, then I suggest making another class function which serves only to increment the counter variable. You should also remove the counter logic from the other functions (sepal_length, sepal_width, etc.)

class Datafeeder:
    ...
    def incr_count(t):
        self.t = t
        self.counter = self.index()
    ...

Then, in your Nengo model, you’ll need to create a node to call this function. Whether or not you call the other function does not matter, just as long as this function is called:

with model:
    ...
    count_node = nengo.Node(data_feeder.incr_count)
    feature_1 = nengo.Node(data_feeder.sepal_length)
    ...