Learn how multiple inheritance uses the method resolution order.
How It Works
Python uses the C3 method resolution order (MRO) to determine the next class searched for an attribute. Method order is inspectable through __mro__, and cooperative methods should delegate with super() consistently.
Mixins usually add small orthogonal capabilities rather than entire competing object models.
Step-by-Step Example
class AuditMixin:
def describe(self):
return "audited"
class BaseService:
def describe(self):
return "service"
class AuditedService(AuditMixin, BaseService):
pass
print(AuditedService().describe())
print([class_type.__name__ for class_type in AuditedService.__mro__])Understanding the Example
- The class groups related state and methods so each instance can manage its own values.
- The function definition gives the operation a reusable name and makes its inputs explicit.
A successful run of this example prints the following output:
audited
['AuditedService', 'AuditMixin', 'BaseService', 'object']Where This Fits in a Real Program
A class is useful when data and the operations that preserve its rules belong together. Distinguish class-level attributes from per-instance state, and make invalid operations fail clearly. Inheritance is not always needed: simpler composition or a standalone function may be easier to maintain.
Practice: Try It Yourself
Swap the parent order of an example class and inspect the resulting MRO.
For this exercise, predict the result before running the changed code. Then explain the difference between the original and modified cases using the actual values, not just whether the program completed.
Further Reading
Read the official Python documentation for complete parameters, return types and exceptions.
Common Beginner Mistakes
- Assuming method lookup randomly chooses among parent classes.
- Directly calling base methods in a cooperative hierarchy and skipping the intended MRO.
Key Takeaways
- Learn how multiple inheritance uses the method resolution order.
- Python uses the C3 method resolution order (MRO) to determine the next class searched for an attribute.
- Mixins usually add small orthogonal capabilities rather than entire competing object models.