"""
Exercise 7.11 from "A primer on...
Modify the class from ex 7.1 with secial methods, to 
make the gi ven use examples work. 
The example below is a slightly improved version of the class, which
includes the parameter values in the output from __str__, not jus 
"a" and "w".
"""


import numpy as np

class F:
    def __init__(self, a, w):
        self.a = a
        self.w = w

    def __call__(self, x):
        return np.exp(-self.a * x) * np.sin(self.w * x)

    def __str__(self):
        return f"exp({self.a}*x)*sin({self.w}*x)"


f = F(a=1.0, w=0.1)
print(f(x = np.pi)) #output: 0.013353835137
f.a = 2
print(f(np.pi)) #output: 0.00057707154012
print(f) #output: exp(-2*x)*sin(0.1*x) 

"""
Terminal> python F2.py 
0.01335383513703555
0.0005770715401197441
exp(2*x)*sin(0.1*x)
"""