Suppose you are working on a Python program to

calculate the area of various shapes. Your program

includes a function called calculate$\_$area$()$ that takes

two parameters: length and width. Inside this function,

you want to calculate the area of a rectangle using the

provided parameters. However, you also have a

variable called pi defined outside of the function, which

is used to calculate the area of a circle.

Your task is to modify the calculate$\_$area$()$ function so

that it can calculate the area of both rectangles and

circles. If the shape is a rectangle, it should return the

area of the rectangle. If the shape is a circle, it should

use the global variable pi to calculate and return the

area of the circle.