Python isinstance() function explained with examples

The Python’s isinstance() function checks whether the object or variable is an instance of the specified class type or data type.

For example, isinstance(name, str) checks if name is an instance of a class str.

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How To Use isinstance() Function in Python

Let’s see the syntax first before moving to the example.

Syntax:

Example

Using isintance() we can verify whether a variable is a number or string. Let’s assume variable num = 90, and you want to check whether num is an instance of an int type.

num = 90
result = isinstance(num, int)
if result:
    print("Yes")
else:
    print("No")

Output:

Yes

As we can see in the output, the isinstance() returned True because num hold an integer value.

Note: If the classinfo argument is not a Class, type, or tuple of types, a TypeError exception is raised.

isinstance() With Built-In Types

As you know, Every value (variable) in Python has a type. In Python, we can use different built-in types such as int, float, list, tuple, strings, dictionary. Most of the time, you want to check the type of value to do some operations. In this case, isinstance() function is useful.

# Check if 80 is an instance of class int
number = 80
print(isinstance(number, int))
# output True

print(isinstance(number, float))
# output False

pi = 3.14
# Check 3.14 is an instance of class float
print(isinstance(pi, float))
# Output True

# Check if (1 + 2j) is an instance of complex
complex_num = 1 + 2j
print(isinstance(complex_num, complex))
# Output True

# Check if 'PYnative' is an instance of class string
name = "PYnative.com"
print(isinstance(name, str))
# Output True

# Check if names is an instance of class list
names = ["Eric", "Scott", "Kelly"]
print(isinstance(names, list))
# Output True

# Check if student_report is an instance of class dict
student_report = {"John": 80, "Eric": 70, "Donald": 90}
print(isinstance(student_report, dict))
# Output True

# Check if names is an instance of class tuple
names = ("Sam", "Kelly", 'Emma')
print(isinstance(names, tuple))
# Output True

# Check if numbers is an instance of class tuple
numbers = {11, 22, 33, 44, 55}
print(isinstance(numbers, set))
# Output True

Note: If we use the isinstance() with any variable or object with a None, it returns False. Let see the simple example of it.

var = None
# empty but not None
s1 = ''
print(isinstance(var, float))
# Output False
print(isinstance(s1, str))
# Output True

isinstance() With Multiple Classes

You can also check the instance with multiple types. Let’s say you have a variable, and you wanted to check whether it holds any numeric value or not, for example, a numeric value can be an int or float.

To verify whether a variable is an instance of one of the specified types, we need to mention all types in a tuple and pass it to the classInfo argument of isinstance().

Example

def check_number(var):
    if isinstance(var, (int, float)):
        print('variable', var, 'is instance of numeric type')
    else:
        print('variable', var, 'is not instance of numeric type')

num1 = 80
check_number(num1)
# Output variable 80 is instance of numeric type

num2 = 55.70
check_number(num2)
# Output variable 55.7 is instance of numeric type

num3 = '20'
check_number(num3)
# Output variable '20' is not instance of numeric type

isinstance() With Python Class

The isinstance() works as a comparison operator, and it compares the object with the specified class type.

You can verify if the emp object is an instance of a user-defined class Employee using the isinstance() function. It must return True.

class Employee:

    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

class Person:

    def __init__(self, name, sex):
        self.name = name
        self.sex = sex

emp = Employee("Emma", 11000)
per = Person("Brent", "male")

# Checking if a emp object is an instance of Employee
print(isinstance(emp, Employee))
# Output True

# Checking if the per object is an instance of Employee
print(isinstance(per, Employee))
# Output False

isinstance() function With Inheritance

The object of the subclass type is also a type of parent class. For example, If Car is a subclass of a Vehicle, then the object of Car can be referred to by either Car or Vehicle. In this case, the isinstance(carObject, Vehicle) will return True.

The isinstance() function works on the principle of the is-a relationship. The concept of an is-a relationship is based on class inheritance.

The instance() returns True if the classinfo argument of the instance() is the object’s class’s parent class.

To demonstrate this, I have created two classes, Developer and PythonDeveoper. Here PythonDeveoper is a sub-class of a Developer class.

class Developer(object):

    # Constructor
    def __init__(self, name):
        self.name = name

    def display(self):
        print("Developer:", self.name, "-")

class PythonDeveloper(Developer):

    # Constructor
    def __init__(self, name, language):
        self.name = name
        self.language = language

    def display(self):
        print("Python Developer:", self.name, "language:", self.language, "-")

# Object of PythonDeveloper
dev = PythonDeveloper("Eric", "Python")
# is PythonDeveloper object an instance of a PythonDeveloper Class
print(isinstance(dev, PythonDeveloper))
# Output True

# is python_dev object an instance of a Developer Class
print(isinstance(dev, Developer))
# Output True

Note: The isinstance() function is beneficial for casting objects at runtime because once you get to know the given class is a subclass of a parent class, you can do casting appropriately if required.

isinstance with Python list

As you know, a Python list is used to store multiple values at the same time. These values can be of any data type like numbers, strings, or any Class objects.

In this section, we will test the following operations with the Python list using the isinstance() function:

• Checking if an object is of type list in python.
• Check if an element of a list is a list.
• Verify if elements of a list are numbers or strings.
• Python check if all elements of a list are the same type

Checking if an object is an instance of a list type

sample_list = ["Emma", "Stevan", "Brent"]
res = isinstance(sample_list, list)
print(sample_list, 'is instance of list?', res)

# Output 'Emma', 'Stevan', 'Brent'] is instance of list? True

Check if an element of a list is a nested list

To check if one of the elements in the list is itself a list. For example, you have the following list, Use the isinstance() to verify if the list contains a nested list

sampleList = ['Emma', 'Stevan', ['Jordan', 'Donald', 'Sam']]

Iterate a list and verify each element’s class, and if it a list type, we can say that the list contains a nested list.

sample_list = ['Emma', 'Stevan', ['Jordan', 'Donald', 'Sam']]
for item in sample_list:
    if isinstance(item, list):
        print("Yes", item, 'is a nested list')

# Output Yes ['Jordan', 'Donald', 'Sam'] is a nested list

Check if elements of a list are numbers or strings

Check each element’s type with multiple numeric types such as int, float, and complex using the isinstance() function.

To find all string variables, Check each element’s type with str type.

sample_list = ['Emma', 'Stevan', 12, 45.6, 1 + 2j, "Eric", ]
number_list = []
string_list = []
for item in sample_list:
    if isinstance(item, (int, float, complex)):
        number_list.append(item)
    elif isinstance(item, str):
        string_list.append(item)

# String List
print(string_list)
# Output ['Emma', 'Stevan', 'Eric']

# Number list
print(number_list)
# Output [12, 45.6, (1+2j)]

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