Snippet of code which shows how the neural network trains.

network-train.py

def train(self, example):
    self.reset_errors()
    error = example.output - self.think(example.inputs)
    self.layers[-1].neurons[0].error = error
    for l in range(len(self.layers) - 1, 0, -1):
        for neuron in self.layers[l].neurons:
            self.layers[l - 1] = neuron.train(self.layers[l - 1])