Rectangle area
Input
Rectangle(3, 4).area()
Output
12.0
Area of a 3x4 rectangle is 12. total_area should return floats (rounded to 6 decimals).
Full lesson preview
Create a Common Interface for Different Subclasses
Design a Shape interface with multiple subclasses and compute total area polymorphically.
Python practice16 minInheritance & PolymorphismIntermediateLast updated April 8, 2026
Problem statement
Define an abstract base class Shape with an area() method. Implement three subclasses: Rectangle(width, height), Circle(radius), and Triangle(base, height). Each subclass should implement area() to return the numeric area.
Then implement total_area(shapes) which accepts a list of Shape instances (or objects implementing area()) and returns the sum of their areas rounded to 6 decimal places (as a float). If the list is empty, return 0.0.
Use math.pi for circle area. total_area should not rely on concrete types — it should call area() on each object (demonstrating polymorphism).
Task
Implement subclasses that conform to a common interface and write a function that operates on a list of heterogeneous objects via that interface.
Examples
Input format
The grader will call total_area([...]) with a list of shape instances.
Output format
Return a float equal to the sum of areas rounded to 6 decimal places. The string representation (str) will be compared to the expected output.
Constraints
- Use math.pi for circle calculations.
- total_area must call area() on each element and return round(sum, 6).
- Do not use any external libraries beyond the Python standard library.
Samples
Sample 1
Input
total_area([Rectangle(3,4), Circle(1)])
Output
15.141593
Rectangle area 12 + circle area pi ≈ 3.141592653589793 => sum ≈ 15.141592653589793 rounded to 6 decimals => 15.141593