2024-heraklion-scientific-patterns/notebooks/01b_Classes_teacher_edition.ipynb

The smell of classes¶

The "data bundle" smell¶

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def momentum(mass, velocity):
    return mass * velocity

def energy(mass, velocity):
    return 0.5 * mass * velocity ** 2

def update_position(velocity, position, dt):
    return position + velocity * dt

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# Naive
mass1 = 10.0
velocity1 = 0.9

mass2 = 12.0
velocity2 = 0.1

print(momentum(mass1, velocity1))
print(momentum(mass2, velocity2))

We have two parameters that will be sent to these functions over and over again: mass and velocity.

Moreover, the parameters cannot be mixed up (e.g. the velocity of one particle with the mass of another).

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Introducing classes as a data bundle template¶

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class Particle:
    pass

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Class methods¶

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def momentum(particle):
    return particle.mass * particle.velocity

print(momentum(particle1))
print(momentum(particle2))

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class Particle:
    def __init__(self, mass, velocity):
        self.mass = mass
        self.velocity = velocity

    # Method here

particle1 = Particle(10.0, 0.9, 0.0)
print(particle1.momentum())

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We have been using class instances and methods all along...

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s = 'A scanner Darkly'
s.capitalize()

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x = set(['apple', 'banana', 'apple', 'pineapple'])
x

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x.union(['banana', 'kiwi'])

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