如何在 Python 3 中的同一绘图上绘制来自多个对象的实例属性

Question

I have a class that generates lists of data from mathematical equations I formulated to model a system over time. The class can take different numbers for the different variables in the equations, therefore you can create objects from the class that have different model output. I would like to plot the output from different objects on the same plot, but when I try to do so I get the following error: ValueError: x and y must have same first dimension, but have shapes (5,) and (10,) . I am plotting using matplotlib. An example of what the code looks like is here:

import matplotlib.pyplot as plt

class Foo:
    def __init__(self, x=[1,2,3,4,5], y=[], var1=None, var2=None):
        self.x = x
        self.y = y
        self.var1 = var1
        self.var2 = var2

    def calculate_y(self, index):
        return (self.var1 + self.var2) * self.x[index]

    def run_calculation(self):
        for i in range (0, len(self.x)):
            self.y.append(self.calculate_y(i))

obj1 = Foo(var1 = 1, var2 = 2)
obj2 = Foo(var1 = 3, var2 = 4)

obj1.run_calculation()
obj2.run_calculation()

plt.figure(1)
plt.plot(obj1.x, obj1.y)
plt.plot(obj2.x, obj2.y)
plt.show()

I am using the lists generated by the class methods from the individual objects to plot. Any idea why I'm getting this error and am unable to plot? Thanks in advance.

Answer 1

Your default argument of an empty list, for some obscure reason, makes it so the same list is appended (get the explanation here ). Change this line so both instances work on separate lists:

self.y = y.copy()

Here's your output: