import matplotlib.pyplot as plt
import numpy as np

class piecewise:
    def __init__(self,time,values):
        if len(time) != len(values):
            print("Wrong arguments to piecewise function")
        self.time = time
        self.values = values

    def __call__(self,t):
        for t_, v_ in zip(self.time,self.values):
            if t < t_:
                return v_
        return 0


#Example code: define and plot a piecewise constant function
phases = [4,28,33]
sigma = piecewise(phases,[20,2,0])

t = np.linspace(0,50,100)
s = []
#class does not work for arrays because of if test, hence a for-loop:
for t_ in t:
    s.append(sigma(t_))
plt.plot(t,s)
plt.show()