How to Use isinstance in Python: Simple Guide with Examples

Use isinstance(object, classinfo) to check if an object is an instance of a class or a tuple of classes. It returns True if the object matches the type, otherwise False. This helps you safely test types before running code that depends on them.

Syntax

The isinstance function takes two arguments:

• object: The variable or value you want to check.
• classinfo: A class, type, or a tuple of classes/types to check against.

It returns True if the object is an instance of the classinfo or any class in the tuple, otherwise False.

python

isinstance(object, classinfo)

Example

This example shows how to check if a variable is an integer or a string using isinstance. It prints messages based on the type.

python

x = 10
if isinstance(x, int):
    print("x is an integer")

name = "Alice"
if isinstance(name, str):
    print("name is a string")

# Check multiple types
value = 3.14
if isinstance(value, (int, float)):
    print("value is a number")

Output

x is an integer
name is a string
value is a number

Common Pitfalls

Some common mistakes when using isinstance include:

• Using type() instead of isinstance() which does not support inheritance checks.
• Passing a single class inside a tuple incorrectly (missing comma).
• Confusing isinstance with issubclass which checks class relationships, not instances.

python

class Animal:
    pass

class Dog(Animal):
    pass

d = Dog()

# Wrong: type() does not consider inheritance
print(type(d) == Animal)  # False

# Right: isinstance() considers inheritance
print(isinstance(d, Animal))  # True

# Wrong: tuple with one class missing comma
print(isinstance(d, (Animal)))  # False

# Right: tuple with one class
print(isinstance(d, (Animal,)))  # True

Output

False
True
False
True

Quick Reference

Usage	Description
isinstance(obj, Class)	Check if obj is instance of Class or subclass
isinstance(obj, (Class1, Class2))	Check if obj is instance of any class in tuple
Returns True or False	Boolean result of the type check

Key Takeaways

Use isinstance(obj, Class) to check an object's type safely including inheritance.

Pass a tuple of classes to check multiple types at once.

Avoid using type() for type checks when inheritance matters.

Remember to include a comma for single-class tuples in isinstance.

isinstance returns True or False, useful for conditional code based on type.