CODEWITHSUNDEEP
pythoninheritanceattributes
euler132
euler132

Reputation: 35

Passing an attribute from a parent to a child class

I am trying to create a child class called Beams which is an extension of the Elements class. The latter computes the length of the element and stores it as an attribute of the Elements class. I would like to somehow pass the length to the child class. What is the right way to do it?

Please note: my code does not instantiate the Elements class directly. Rather its attributes are used in the instances of the Beam class through inheritance.


class Elements:

    def __init__(self,number,start_node,end_node,e_modulus,cs_area):

        self.number = number
        self.start_node = start_node
        self.end_node = end_node
        self.e_modulus = e_modulus

        d_x = end_node.x_glob - start_node.x_glob
        d_y = end_node.y_glob - start_node.y_glob

        self.length = mt.sqrt(d_x**2 + d_y**2)
        self.alpha = mt.atan2(d_y, d_x)

        r1 = mt.cos(self.alpha)
        r2 = mt.sin(self.alpha)

        self.rot_matrix = np.array([[r1,  r2, 0, 0,   0,  0],
                                   [-r2, r1, 0, 0,   0,  0],
                                   [0,   0,  1, 0,   0,  0],
                                   [0,   0,  0, r1,  r2, 0],
                                   [0,   0,  0, -r2, r1, 0],
                                   [0,   0,  0, 0,   0,  1]])


class Beam(Elements):

    def __init__(self,number,start_node,end_node,e_modulus,cs_area,second_mom_of_area):
        super().__init__(number,start_node,end_node,e_modulus,cs_area)
        self.second_mom_of_area = second_mom_of_area


        k1 = (e_modulus*cs_area)/length
        k2 = (12*e_modulus*second_mom_of_area)/(length**3)
        k3 = (6*e_modulus*second_mom_of_area)/(length**2)
        k4 = (4*e_modulus*second_mom_of_area)/(length)
        k5 = (2*e_modulus*second_mom_of_area)/(length)

        self.loc_stiff_matrix = np.array([[ k1,   0,   0, -k1,   0,   0],
                                         [  0,  k2,  k3,   0, -k2, -k3],
                                         [  0,  k3,  k4,   0, -k3,  k5],
                                         [-k1,   0,   0,  k1,   0,   0],
                                         [  0, -k2, -k3,   0,  k2,   0],
                                         [  0,  k3,  k5,   0, -k3,  k4]])

Upvotes: 0

Views: 789

Answers (1)

pcko1
pcko1

Reputation: 981

Everything you define in your parent class is inherited by the child and, unless explicitly modified in the body of the child, they are directly accessible as attributes.

In your case:

beam = Beam(**kwargs)

print(beam.length)
# or
print(getattr(beam, "length"))

should work.

Upvotes: 1

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