Python program that calculates the area of a circle based on the radius entered by the user.

areaByRadius.py

# Python exercise: https://www.w3resource.com/python-exercises/python-basic-exercises.php
#
# 4. Write a Python program that calculates the area of a circle based on the radius entered by the user.
#
# Some online compilers do not allow importing sys.
# Remove the following line in such case, and set sysIsAvailable to False.
from sys import exit
isSysAvailable = True

from math import pi

r = ""

while r.isdigit() is False:
    if r == "Q" or r == "q":
        print("exit")
        if isSysAvailable is True:
            exit()
        else:
            r = "0"
            continue

    elif r != "":
        print("Invalid input. Press Q and hit Enter to exit.")

    r = input("Please input the radius of the circle:\n")

if r != "0":
    area = pi * (float(r)**2)
    # The question prefers unformatted number, but here it is in two decimal places:
    print(format(area, ".2f"))
    # If you need the preferred answer, comment the above line and uncomment the following line.
    # print(area)