def integral(f, start, stop, width=0.0001):
    total = 0 # The accumulator
    i = start # The loop counter (counts by width)
    while i < stop:
        total += f(i) * width
        i += width
    return total

# Test routine
def f_easy(x):
    return 4

print("Should be 16:  ", integral(f_easy, 0, 4));

def square_function(x):
    return x**2
print(integral(square_function, 1, 4))

: