Limitation in output generated by a class

Let's say that I want to create a class circle that, provided a value r and a value delta_r, can calculate the annulus area of a couple of circles. Afterwards, using this class, I want to create a list with several couples of circles.

How can I add a condition, built in the class, that allows to append values only if r < 7? So that, in the example, the list C is still created but includes only results till r=6.

import numpy as np
from numpy import pi

class circle:
    def __init__(self, r=1, delta_r=0.1):
        self.r = r
        self.delta_r = delta_r

        self.area1 = pi*r**2
        self.area2 = pi*(r+delta_r)**2
        self.annulus = self.area2 - self.area1

C_range = np.arange(1, 10)
C = []
for n in C_range:
    C.append(circle(n, 0.2))