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Can You Create Your Own Neural Network Using Python?

 A novice's manual for understanding the internal activities of Deep Learning 

Update: When I composed this article a year prior, I didn't anticipate that it should be this mainstream. From that point forward, this article has been seen more than multiple times, with more than 30,000 applauds. It has likewise made it to the first page of Google, and it is among the initial not many query items for 'Neural Network'. A considerable lot of you have connected with me, and I am profoundly lowered by the effect of this article on your learning venture.

This article additionally grabbed the attention of the editors at Packt Publishing. Not long after this article was distributed, I was offered to be the sole writer of the book Neural Network Projects with Python. Today, I am glad to impart to you that my book has been distributed!

The book is a continuation of this article, and it covers start to finish execution of neural organization projects in regions, for example, face acknowledgment, feeling investigation, commotion expulsion and so forth Each section includes an interesting neural organization engineering, including Convolutional Neural Networks, Long Short-Term Memory Nets and Siamese Neural Networks. In case you're hoping to make a solid AI portfolio with profound learning projects, do consider getting the book!

You can get the book from Amazon: Neural Network Projects with Python

Inspiration: As a component of my own excursion to acquire a superior comprehension of Deep Learning, I've chosen to construct a Neural Network without any preparation without a profound learning library like TensorFlow. I accept that understanding the internal operations of a Neural Network is imperative to any hopeful Data Scientist.

This article contains what I've realized, and ideally, it'll be helpful for you also!

What's a Neural Network?

Most starting writings to Neural Networks raise cerebrum analogies while depicting them. Without diving into mind analogies, I think that its simpler to just portray Neural Networks as a numerical capacity that guides an offered contribution to an ideal yield.

Neural Networks comprise of the accompanying parts

An information layer, x

A discretionary measure of covered up layers

A yield layer, ŷ

A bunch of loads and predispositions between each layer, W and b

A decision of enactment work for each secret layer, σ. In this instructional exercise, we'll utilize a Sigmoid initiation work.

The chart beneath shows the engineering of a 2-layer Neural Network (note that the info layer is normally avoided when including the number of layers in a Neural Network)


Making a Neural Network class in Python is simple.

class NeuralNetwork:

    def __init__(self, x, y):

        self.input      = x

        self.weights1   = np.random.rand(self.input.shape[1],4) 

        self.weights2   = np.random.rand(4,1)                 

        self.y          = y

        self.output     = np.zeros(y.shape)

Preparing the Neural Network

The yield ŷ of a straightforward 2-layer Neural Network is:


You may see that in the condition over, the loads W and the inclinations b are the solitary factors that influence the yield ŷ.

Normally, the correct qualities for the loads and predispositions decide the strength of the expectations. The cycle of calibrating the loads and predispositions from the info information is known as preparing the Neural Network.

Every emphasis of the preparation cycle comprises of the accompanying advances:

  • Ascertaining the anticipated yield ŷ, known as feedforward
  • Refreshing the loads and predispositions, known as backpropagation

The consecutive diagram beneath represents the cycle.



As we've found in the consecutive diagram above, feedforward is simply basic math and for a fundamental 2-layer neural organization, the yield of the Neural Network is:


How about we add feedforward work in our python code to do precisely that. Note that for straightforwardness, we have expected the inclinations to be 0.

class NeuralNetwork:

    def __init__(self, x, y):

        self.input      = x

        self.weights1   = np.random.rand(self.input.shape[1],4) 

        self.weights2   = np.random.rand(4,1)                 

        self.y          = y

        self.output     = np.zeros(self.y.shape)

        def feedforward(self):

        self.layer1 = sigmoid(, self.weights1))

        self.output = sigmoid(, self.weights2))

Notwithstanding, we actually need an approach to assess the "integrity" of our expectations (for example how distant are our expectations)? The Loss Function permits us to do precisely that.

Misfortune Function

There are numerous accessible misfortune capacities, and the idea of our concern should direct our decision of misfortune work. In this instructional exercise, we'll utilize a straightforward amount of-squares blunder as our misfortune work.

That is, the amount of-squares mistake is essentially the amount of the contrast between each anticipated worth and the real worth. The thing that matters is squared so we measure the outright worth of the distinction.

Our objective in preparing is to track down the best arrangement of loads and predispositions that limits the misfortune work.


Since we've estimated the mistake of our expectation (misfortune), we need to figure out how to proliferate the blunder back, and to refresh our loads and predispositions.

To realize the proper sum to change the loads and predispositions by, we need to know the subsidiary of the misfortune work regarding the loads and inclinations.

Review from math that the subsidiary of a capacity is essentially the incline of the capacity.

On the off chance that we have the subsidiary, we can just refresh the loads and inclinations by expanding/diminishing with it(refer to the graph above). This is known as slope drop.

Notwithstanding, we can't straightforwardly ascertain the subsidiary of the misfortune work regarding the loads and predispositions in light of the fact that the condition of the misfortune work doesn't contain the loads and inclinations. Hence, we need the chain rule to assist us with computing it.

Golly! That was monstrous however it permits us to get what we required — the subsidiary (slant) of the misfortune work concerning the loads, so we can change the loads appropriately. 

Since we have that, we should add the backpropagation work into our python code.

class NeuralNetwork:
def __init__(self, x, y):
self.input = x
self.weights1 = np.random.rand(self.input.shape[1],4)
self.weights2 = np.random.rand(4,1)
self.y = y
self.output = np.zeros(self.y.shape)
def feedforward(self):
self.layer1 = sigmoid(, self.weights1))
self.output = sigmoid(, self.weights2))
def backprop(self):
# application of the chain rule to find derivative of the loss function with respect to weights2 and weights1
d_weights2 =, (2*(self.y - self.output) * sigmoid_derivative(self.output)))
d_weights1 =, (*(self.y - self.output) * sigmoid_derivative(self.output), self.weights2.T) * sigmoid_derivative(self.layer1)))
# update the weights with the derivative (slope) of the loss function
self.weights1 += d_weights1
self.weights2 += d_weights2

For a more profound comprehension of the use of math and the chain rule in backpropagation, I emphatically suggest this instructional exercise by 3Blue1Brown.

For a more profound comprehension of the use of math and the chain rule in backpropagation, I firmly suggest this instructional exercise by 3Blue1Brown.

Assembling everything

Since we have our total python code for doing feedforward and backpropagation, we should apply our Neural Network to a model and perceive how well it does.

Our Neural Network ought to become familiar with the ideal arrangement of loads to address this capacity. Note that it isn't actually paltry for us to work out the loads just my assessment alone.

We should prepare the Neural Network for 1500 emphasizes and see what occurs. Taking a gander at the misfortune per cycle chart beneath, we can unmistakably see the misfortune monotonically diminishing towards a base. This is predictable with the inclination drop calculation that we've talked about before.


How about we take a gander at the last expectation (yield) from the Neural Network after 1500 emphases.


We did it! Our feedforward and backpropagation calculation prepared the Neural Network effectively and the forecasts merged on the genuine qualities.

Note that there's a slight contrast between the expectations and the genuine qualities. This is attractive, as it forestalls overfitting and permits the Neural Network to sum up better inconspicuous information.

What's Next?

Luckily for us, our excursion isn't finished. There's still a lot to find out about Neural Networks and Deep Learning. For instance:

  • What other enactment capacity would we be able to utilize other than the Sigmoid capacity?
  • Utilizing a learning rate when preparing the Neural Network
  • Utilizing convolutions for picture arrangement errands

I'll compose more on these points soon, so follow me on Medium and look out for them!

Last Thoughts


I've positively taken in a ton composing my own Neural Network without any preparation.


Albeit Deep Learning libraries, for example, TensorFlow and Keras make it simple to construct profound nets without completely understanding the internal functions of a Neural Network, I find that it's valuable for hopeful information researchers to acquire a more profound comprehension of Neural Networks.


This activity has been incredible speculation of my time, and I trust that it'll be helpful for you also!

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