import numpy as np
from math import pi

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

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

f = F(a=1.0, w=0.1)
print(f.value(x=pi))
f.a = 2
print(f.value(x=pi))

"""
Terminal> python F.py
0.01335383513703555
0.0005770715401197441
"""

"""
#Improved version of the class, 
#with __call__ and __str__ 
#special methods:

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

    def __all__(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)'

#usage:
f = F(a=1.0, w=0.1)
print(f(x=pi))  
print(f)     
"""