"""
Exercise 7.11 from "A primer on..."
Modify the class from ex 7.1 to support
the given usage. We see that the
class needs a __call__ method to support
calls like f(x=pi), as well as a __str__ 
method that returns the function expression, for
pretty print. 
"""

from math import pi
import numpy as np

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

    def __call__(self, x):
        a = self.a
        w = self.w
        return np.exp(-a * x) * np.sin(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 = pi))
f.a = 2.0
print(f(x = pi))
print(f)
#output: exp(-a*x)*sin(w*x)
"""
Terminal> python F2.py 
0.01335383513703555
0.0004931861122731331
exp(-2.05*x)*sin(0.1*x)
"""