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In this article, We will learn what does isinstance() function does in Python and how to use it. The Python isinstance() function is used to check whether the object or variable is an instance of the specified class type or data type.
Further reading
For example, you have a variable number = 90, and you want to check the number is an instance of an int type. You can check this using isinstance() function.
Let’s understand how to use isinstance() function with the help of a simple example.
marks = 90
result = isinstance(marks, int)
if result :
print("Yes! given variable is an instance of type int")
else:
print("No! given variable is not an instance of type int")Output:
Yes! given varible is an instance of type int
Using Python isinstance(), you can do the followings:
isinstance(object, classinfo)The isinstance() function checks if the object argument is an instance or subclass of classinfo class argument.
isinstance Parameters:
Return Value from isinstance():
If an object or variable is of a specified type, then isinstance() return true otherwise false.
As you know, Every value (variable) in Python has a type. Different built-in types in Python are Numbers, List, Tuple, Strings, Dictionary. Most of the time you want to check the type of a value to do some operations on it. In this case, isinstance() function is useful.
In this example, we are using isinstance() function to check instance with the String type, number type, dict type, list type.
number = 80
pi = 3.14
name = "pynative.com"
complexNum = 1+2j
sampleList = ["Eric", "Scott", "Kelly"]
studentDict = {"John":80, "Eric":70, "Donald":90}
sampleTuple = ("Sam","Developer", 10000)
sampleSet = {11, 22, 33, 44, 55}
flag = isinstance(number, int)
print(number,'is an instance of int?', flag)
flag = isinstance(pi, float)
print(pi,'is an instance of float?', flag)
flag = isinstance(complexNum, complex)
print(complexNum, "is an instance of a complex number?", flag)
flag = isinstance(name, str)
print(name,'is an instance of String?', flag, "\n")
flag = isinstance(sampleList, list)
print(sampleList,'is instance of list?', flag)
flag = isinstance(studentDict, dict)
print(studentDict,'is instance of Dictionary?', flag)
flag = isinstance(sampleTuple, tuple)
print(sampleList,'is instance of Tuple?', flag)
flag = isinstance(sampleSet, set)
print(studentDict,'is instance of Set?', flag)Output:
80 is an instance of int? True
3.14 is an instance of float? True
(1+2j) is an instance of a complex number? True
pynative.com is an instance of String? True
['Eric', 'Scott', 'Kelly'] is instance of list? True
{'John': 80, 'Eric': 70, 'Donald': 90} is instance of Dictionary? True
['Eric', 'Scott', 'Kelly'] is instance of Tuple? True
{'John': 80, 'Eric': 70, 'Donald': 90} is instance of Set? True
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 int or float. You can check this variable with multiple types. To do this, you need to mention all types in a tuple and pass it as the isinstance’s classInfo argument.
Let’s see this with an example.
firstNumber = 80
secondNumber = 55.70
result = isinstance(firstNumber, (int, float))
print(firstNumber,'is an instance of int or float?', result)
result = isinstance(secondNumber, (int, float))
print(secondNumber,'is an instance of int or float?', result)
Output:
80 is an instance of int or float? True 55.7 is an instance of int or float? True
As you can see we mentioned two types in tuple format to check whether a given variable is a type of mentioned type in the tuple. You can add as many types in the tuple as you can want.
A isinstance() function test object is of a specified class type. isinstance() is working as a comparison operator because it compares the object with the specified class type.
The isinstance result will be true if the object is an instance of the given class type:
I have created an Employee class and checking object is an instance of class Employee.
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")
print("Checking emp object is an instance of Employee")
if isinstance(emp, Employee) :
print("Yes! given object is an instance of class Employee\n")
else:
print("No! given object is not an instance of class Employee")
print("Checking per object is an instance of Employee")
if isinstance(per, Employee) :
print("Yes! given object is an instance of class Employee")
else:
print("No! given object is not an instance of class Employee\n")Output:
Checking emp object is an instance of Employee Yes! a given object is an instance of class Employee Checking per object is an instance of Employee No! given object is not an instance of class Employee
As we know the object of the subclass type is also a type of parent class. For example, If Car is a subclass of Vehicle then the object of Car class can be referred by either Car or Vehicle.
Then 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.
To demonstrate this, I have created two classes Developer and PythonDeveoper, Here PythonDeveoper is a sub-class of a Developer class.
isinstance() function will also be true if the object is an instance of a subclass of the given class type:
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, "-")
dev = Developer("Jhon") # An Object of Developer
dev.display()
result = isinstance(dev, Developer)
print("is an instance of a Developer Class? ", result, "\n")
pythonDev = PythonDeveloper("Eric", "Python") # An Object of PythonDeveloper
pythonDev.display(),
result = isinstance(pythonDev, Developer)
print("is an instance of a Developer Class? ", result)Output:
Developer: Jhon - is an instance of a Developer Class? True Python Developer: Eric language: Python - is an instance of a Developer Class? 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.
As you know, a Python list is used to store multiple values at the same time. These values can be of any type like numbers, strings or any class objects.
In this section, we are performing the following operations with Python list using the isinstance() function:
Checking if an object is of type list in python
sampleList = ["Emma", "Stevan", "Brent"]
res = isinstance(sampleList, list)
print(sampleList,'is instance of list?', res)Output:
['Emma', 'Stevan', 'Brent'] is instance of list? True
Check if an element of a list is a list
To check if an element in the list is itself a list we can use isinstance(). For example, you have the following list and you want to check is there any element is of type list in this list.
sampleList = ['Emma', 'Stevan', ['Jordan','Donald', 'Sam']]You need to iterate a list to check each variable’s type and if it a list type we can say that the list itself contains a list.
sampleList = ['Emma', 'Stevan', ['Jordan','Donald', 'Sam']]
for item in sampleList:
if isinstance(item, list):
print("Yes", item,'is list item is an instance of the given list')Output:
Yes ['Jordan', 'Donald', 'Sam'] is list item is an instance of the list
Check if elements of a list are numbers or strings
To find numbers from the given list we need to check each element with multiple numeric types such as int, float, long and complex type using isinstance() function.
To find all string variables we can check each element type with str type.
sampleList = ['Emma', 'Stevan', 12, 45.6, 1+2j, "Eric", ]
numberList = []
stringList = []
for item in sampleList:
if isinstance(item, (int, float, complex)):
numberList.append(item)
elif isinstance(item, str):
stringList.append(item)
print("String List \n", stringList)
print("Number List \n", numberList)Output:
String List ['Emma', 'Stevan', 'Eric'] Number List [12, 45.6, (1+2j)]
If we use isinstance with any variable or object that has a null or None value it returns false. Let see the simple example of it.
var = None
result = isinstance(var, float)
print(var,'is an instance of float?', result, "\n")Output:
None is an instance of float? False
