int object is not subscriptable (python)

I'm new using Python and I do not know why it's giving the error:

  

Traceback (most recent call last):     File "C: \ Users \ Gabriel \ Desktop \ Perceptron.py", line 51, in       print (perceptron (max_it, errors, alpha, inputs, outputs))     File "C: \ Users \ Gabriel \ Desktop \ Perceptron.py", line 45, in perceptron       outputs.append (calculatePotential (inputs [i], weights [i], bias))     File "C: \ Users \ Gabriel \ Desktop \ Perceptron.py", line 15, in calculatePotential       u = inputs [0] * weights [0] + inputs [1] * weights [1] + bias   TypeError: 'int' object is not subscriptable

Code:

    # Perceptron em Python 
# Gabriel Augusto - 14-11-2017

#Variables
max_it = 3      #epoque
errors = [1, 0, 0, 0]
inputs = [[0, 0], [0, 1], [1, 0], [1, 1]]
labels = [-1, -1, -1, 1]
outputs = []
alpha = 0.1


#activation potential
def calculatePotential(inputs, weights, bias):  
    u = inputs[0] * weights[0] + inputs[1] * weights[1] + bias
    if (u <= 0):
        return -1
    else:
        return 1

def startWeights(max_it):
    weights = []
    for x in range(0, max_it):
        weights.append(0)
    return weights

def sumErrors(errors):
    sumErrors = 0
    for i,j in enumerate(errors):
        sumErrors += j
    return sumErrors


#function Perceptron
def perceptron(max_it, erros, alpha, inputs, outputs):

    #start weights
    weights = startWeights(max_it)

    bias = 0
    t = 1   

    #while (t < max_it and sumErrors(errors) > 0):
    for i in range(4):
        outputs.append(calculatePotential(inputs[i], weights[i], bias))
    return outputs


print(perceptron(max_it, errors, alpha, inputs, outputs))