"""
Ex 7.11 from A Primer on...
"""
from math import *

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

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

    def __str__(self):
        return 'exp(-a*x)*sin(w*x)'

"""
Simple demonstration that the __call__ and
__str__ methods work:
"""
f = F(a=1.0, w=0.1)
print(f(pi))
print(f)

"""
Terminal> python F2.py 
0.01335383513703555
exp(-a*x)*sin(w*x)
"""