A simple Python code

I am currently learning Python and writing a simple code that includes: importing packages, input, output, while loop, loop termination, if conditional judgment, and two types of formatted strings.

import math
print("== --enter a radius to calculate the area-- ==")
num = input("please enter a radius :")
while True:
if num.isdigit():
  r = float(num)
  break
else:
  print("{:s }not a number.".format(num))
  r = input("please enter a number :")
s = math.pi * r ** 2
#format string 
print("the radius is" + num + "the circle has an area of :" + str(round(s, 2)) + "。")       #string concatenation 
print("the radius is %s the circle has an area of :%.2f。" % (num, s))                         #apply % operator 
print("the radius is{ :s }the circle has an area of :{:.2f}。".format(num, s))                 # format method 
print(f"the radius is{ num }the circle has an area of :{s:.2f}。")                             # f string, Python3. added in version 6