This rule raises an issue when performing direct type comparisons instead of using the
Why is this an issue?
In Python, using the
isinstance() function is generally preferred over direct type comparison for several reasons:
- Compatibility with inheritance:
isinstance() considers inheritance hierarchy, whereas direct type comparison does
not. This means that
isinstance() can handle cases where an object belongs to a subclass of the specified type, making your code more
flexible and robust. It allows you to write code that can work with objects of different but related types.
- Support for duck typing: Python follows the principle of "duck typing," which focuses on an object’s behavior rather than its
isinstance() enables you to check if an object has certain behavior (by checking if it belongs to a particular class or
subclass) rather than strictly requiring a specific type. This promotes code reusability and enhances the flexibility of your programs.
- Code maintainability and extensibility: By using
isinstance(), your code becomes more maintainable and
extensible. If you directly compare types, you would need to modify your code whenever a new subtype is introduced or the inheritance hierarchy is
changed. On the other hand,
isinstance() allows your code to accommodate new types without requiring any modifications, as long as they
exhibit the desired behavior.
- Polymorphism and interface-based programming:
isinstance() supports polymorphism, which is the ability of
different objects to respond to the same method calls. It allows you to design code that interacts with objects based on their shared interface
rather than their specific types. This promotes code reuse and modularity, as you can write functions and methods that operate on a range of
- Third-party library compatibility: Many third-party libraries and frameworks in Python rely on
type checking and handling different types of objects. By using
isinstance(), your code becomes more compatible with these libraries
and frameworks, making it easier to integrate your code into larger projects or collaborate with other developers.
In summary, using
isinstance() over direct type comparison in Python promotes flexibility, code reusability, maintainability,
extensibility, and compatibility with the wider Python ecosystem. It aligns with the principles of object-oriented programming and supports the
dynamic nature of Python. It is also recommended by the PEP8 style guide.
How to fix it
isinstance() function instead of performing direct type comparisons.
Noncompliant code example
if type(a) == MyClass: # Noncompliant
if isinstance(a, MyClass):