Composite Pattern in Python
Composite represents tree structures while letting clients handle leaves and containers uniformly.
What is Composite Pattern?
Composite represents tree structures while letting clients handle leaves and containers uniformly.
Treat individual objects and object groups through the same interface.
When should you use it?
- Solve recurring object-design problems with proven structures.
- Decouple responsibilities so code is easier to extend and test.
- Use shared design vocabulary when discussing architecture with a team.
Example code
main.py
class Number:
# Composite: leaves and containers expose the same operation.
def __init__(self, value): self.value = value
def total(self): return self.value
class Sum:
def __init__(self, *children): self.children = children
def total(self):
# Treat leaves and nested groups uniformly.
return sum(child.total() for child in self.children)
expression = Sum(Number(1), Sum(Number(2), Number(3)))
print(expression.total())Expected output
6How it works
Number and Sum both implement total, allowing nested groups to be evaluated recursively.
Change the values and run the program in the CodeUtility online Python compiler without installing Python locally.
Practice exercises
Modify the runnable example with the exercises below to build understanding beyond copying the result.
- Replace the sample domain while preserving the pattern structure.
- Compare the pattern with a simpler implementation and explain the tradeoff.
- Write tests for each participant before adding another implementation.