Python isinstance()

In Python, the isinstance() function checks whether an object is an instance of a specified type, class, or a tuple of classes. If it is, the function returns True, otherwise it returns False. This check is useful for type validation in functions, debugging, and ensuring safe operations on data structures.

Syntax

isinstance(object, class)

Parameters:

• object: The object, or a reference to the object, to be tested.
• class: The type to be used by the function in this assertion (e.g. list, set, etc.).

Return value:

If the given object is of the designated value type, the isinstance() function returns True, otherwise it returns False.

Example 1: Basic Usage of isinstance()

This example uses the isinstance() function to check if the given value is a string:

value = "Hello World!"

if isinstance(value, str):
  print("String")
else:
  print("Not a string")

Copy to clipboard
Copy to clipboard

Here is the output:

String

Copy to clipboard
Copy to clipboard

Example 2: Checking Against Multiple Types Using isinstance()

This example uses the isinstance() function to check if the given value is a list or tuple:

data = [1, 2, 3]

if isinstance(data, (list, tuple)):
  print("List or tuple")
else:
  print("Not a list or tuple")

Copy to clipboard
Copy to clipboard

Here is the output:

List or tuple

Copy to clipboard
Copy to clipboard

Codebyte Example: Custom Class Type Checking Using isinstance()

This codebyte example uses the isinstance() function to check if the given object belongs to a user-defined class:

Visit us
Visit us
Hide code
Code
Output
Hide output
Loading...
Copy to your clipboard
Copy Codebyte
Run

Since the given object pet belongs to the user-defined class Dog, the code will return True.

Frequently Asked Questions

1. What is the difference between isinstance() and type()?

type() checks for the exact type and does not consider inheritance, whereas isinstance() is preferred when you want to account for subclasses.

2. Is isinstance() faster or slower than type()?

Generally, type() is faster because it’s a simpler check, but isinstance() is more flexible and recommended in most cases due to its support for inheritance.

3. Can isinstance() be used with abstract base classes?

Yes, isinstance() can be used with abstract base classes. This is common when working with interfaces or abstract classes using the abc module.