human
I am working on the file "Day_02/01_ObjectOrientedProgramming/00_Object_Oriented_Programming.ipynb".
The first task is:
In the code example, we have a Circle class. We define three new methods. 

area()
setRadius()
getRadius()

The area() method returns the area of a circle.  The getRadius() method returns the current radius. 
Special Methods
Classes in Python programming language can implement certain operations with special method names. These methods are not called directly, but by a specific language syntax. This is similar to what is known as operator overloading in C++ or Ruby.
Can you write Python program for it?
assistant
#Here is known as operator overloading in C++ or Ruby.

class Book:
   def __init__(self, title, author, pages):
      print "A book is created"
      self.title = title
      self.author = author
      self.pages = pages

   def __str__(self):
      return "Title:%s , author:%s, pages:%s " % \
              (self.title, self.author, self.pages)

   def __len__(self):
      return self.pages

   def __del__(self):
      print "A book is destroyed"

book = Book("Inside Steve's Brain", "Leander Kahney", 304)

print book
print len(book)
del book