My dictionary has 9 items yet when iterating with for there are only eight

Question

Here is my code:

trainingSet = {"0,0":0, "1,0":1, "2,0":1, "0,1":0, "1,1":1, "1,2":0, "2,0":0, "2,1":0, "2,2":1}

for k,expectedOutput in trainingSet.iteritems():
    print 1
    coordinates = k.split(",")
    network.layers[0].neurons[0].value = float(coordinates[0])
    network.layers[0].neurons[1].value = float(coordinates[1])
    output = network.calculateOutput()

The output is:

1
1
1
1
1
1
1
1
# 8 lines

How is that possible? There are 9 items in the trainingSet dictionary. Shouldn't the output be:

1
1
1
1
1
1
1
1
1
# 9 lines

Answer 1

You have the key "2,0" twice:

... "2,0":1, "0,1":0, "1,1":1, "1,2":0, "2,0":0  ...
     ^^^                                 ^^^

The keys in a dictionary must be unique. If you want to have a key more than once with different values you need to use a different data structure. You could use for example a list of tuples, or a dictionary from the key to a list of values.

More likely though I guess you just mixed up the numbers and you actually meant something like this:

trainingSet = {
    "0,0" : 0, "1,0" : 1, "2,0" : 1,
    "0,1" : 0, "1,1" : 1, "2,1" : 0,
    "0,2" : 0, "1,2" : 0, "2,2" : 1
}