Circle

I want you to make a class that represents a circle.

The circle should have a radius, a diameter, and an area. It should also have a nice string representation.

For example:

>>> c = Circle(5)
>>> c
Circle(5)
>>> c.radius
5
>>> c.diameter
10
>>> c.area
78.53981633974483

Additionally the radius should default to 1 if no radius is specified when you create your circle:

>>> c = Circle()
>>> c.radius
1
>>> c.diameter
2

There are three bonuses for this exercise.

Bonus 1