Python isinstance() Function

Python isinstance() function is used to check whether the given object is an instance of that class. If the object belongs to the class, it returns True. Otherwise returns False. It also returns true if the class is a subclass.

The isinstance() function takes two arguments object and classinfo and returns either True or False. The signature of the function is given below.

Syntax:

Parameters

object: It is an object of string, int, float, long or custom type.

classinfo: Class name.

Return

It returns boolean either True or False.

Let's see some examples of isinstance() function to understand it's functionality.

Python Isinstance() Examples:

We utilize the isinstance() function to check whether various variables are instances of their separate data types or classes.

1. Integer

Code

# Check if an integer is an int
n = 100
print(isinstance(n, int))  

Output:

True

2. Float

Code

# Check if a float is a float
pi = 3.14159
print(isinstance(pi, float))  

Output:

True

3. String

Code

# Check if a string is a string
name = "Johnny"
print(isinstance(name, str))  

Output:

True

4. List

Code

# Check if a list is a list
colours = ["blue", "black", "brown"]
print(isinstance(colours, list))  

Output:

True

5. Dictionary

Code

# Check if a dictionary is a dict
person = {"name": "Ayan", "age": 30}
print(isinstance(person, dict))  

Output:

True

6. Tuple

Code

# Check if a tuple is a tuple
point = (1, 5)
print(isinstance(point, tuple))  

Output:

True

7. Set

Code

# Check if a set is a set
digits = {1, 2, 3, 4,5,6,7,8}
print(isinstance(digits, set))  

Output:

True

8. Class

Code

# Check if a custom class instance is an instance of that class
class Bike:
    pass

my_bike = Bike()
print(isinstance(my_bike, Bike))  

Output:

True

Let's see some more examples of isinstance() function to understand it's functionality.

Python isinstance() Function Example 1

Here, we are passing object and class to the function which returns True only if the object belongs to the class. See the below example.

Code

# Python isinstance() function example  
class Student:  
    id = 101  
    name = "John"  
    def __init__(self, id, name):  
        self.id=id  
        self.name=name  
  
student = Student(1010,"John")  
lst = [ 12,34,5,6,767 ]  
# Calling function   
print(isinstance(student, Student)) # isinstance of Student class  
print(isinstance(lst, Student))  

Output:

True
False

Python isinstance() Function Example 2

isinstance() can be utilized to check on the off chance that an object is an instance of a class that carries out a specific interface. We can characterize an interface as a class that determines a bunch of techniques that different classes execute.

Code

# Python isinstance() function example  
class Animal:
    def speak(self):
        raise NotImplementedError

class Dog(Animal):
    def speak(self):
        return "Woof!"

class Cat(Animal):
    def speak(self):
        return "Meow!"

def make_animal_speak(animal):
    if isinstance(animal, Animal):
        return animal.speak()
    else:
        raise ValueError("Object is not an Animal")

my_dog = Dog()
my_cat = Cat()

print(make_animal_speak(my_dog))  
print(make_animal_speak(my_cat))  

Output:

"Woof!"
"Meow!"

Python isinstance() Function Example 3

This function also returns True if the object is of subclass and class is a parent class. See, how it works in the below example.

Code

# Python isinstance() function example  
# Declaring variables  
  
class NumericList(list):  
    def __init__(self):  
        return None  
  
num = NumericList()  
# Calling function   
print(isinstance(num, NumericList)) # True  
print(isinstance(num, list)) # True  

Output:

True
True

Conclusion:

In conclusion, the isinstance() function is a helpful built-in Python function that permits us to check whether an object is an instance of a predefined class or subclass. This can be especially valuable while working with code that includes various data types, or while writing libraries or APIs that need to deal with a great many input types. By utilizing isinstance(), one can guarantee that our code acts accurately for different input types and is more vigorous generally speaking.

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