`type()` vs. `isinstance()` in Python: When to Use Which?

Differences Between type() and isinstance()

The type() and isinstance() functions in Python perform type checking, but with distinct characteristics.

type()

The type() function evaluates the type of an object and returns the type object itself. It checks for the exact type of the object without considering inheritance.

isinstance()

In contrast, isinstance() verifies if an object is an instance of a specified type or its subclasses. It supports inheritance, meaning that an object of a derived class will successfully pass the isinstance() check for the base class.

Code Comparison

Consider the following code snippets:

# Using type()
import types

if type(a) is types.DictType:
    do_something()
if type(b) in types.StringTypes:
    do_something_else()

# Using isinstance()
if isinstance(a, dict):
    do_something()
if isinstance(b, str) or isinstance(b, unicode):
    do_something_else()

The type() checks will succeed only if the object is an instance of the exact type, while isinstance() will succeed if the object is an instance of the specified type (dict in the example) or any of its subclasses.

Advantages of isinstance()

• Support for inheritance: Checks for membership in a class hierarchy.
• Simplicity and readability: More concise and intuitive compared to type() checks.

Considerations

• Performance: type() may be slightly faster than isinstance() for simple checks.
• Robustness: isinstance() handles inheritance and is less error-prone.
• Conflicting roles: Relying heavily on instanceof() may hinder the ability to check for specific types in certain scenarios.

Conclusion

Generally, isinstance() is preferred for most type checking scenarios as it seamlessly supports inheritance and is more readable than type() checks. For precise checks where inheritance is not a concern, type() can be used.

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