How do you check if a variable is initialized in Python?

The Python’s

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

For example,

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

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

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

Also, Solve: Python Basic Exercise and Beginners Quiz

Table of contents

How To Use isinstance() Function in Python

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

Syntax:

isinstance(object, classinfo)

• It takes two arguments, and both are mandatory.
• The

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

  2 function checks if the

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

  7 argument is an instance or subclass of

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

  8 class argument

Using

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

1. Pass object to isinstance()

   Pass the variable you want to check as

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

   7 argument to the

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

   2. Here the object can be any class object or any variable name

2. Specify the Class or Type name as a

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

   8 argument

   For example,

   Yes

   3 to check if

   Yes

   4 is an instance of a class

   Yes

   5.
   

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

   8 is a type name or Class name you want to check against the variable. Here you can specify data type name or Class name.
   You can also pass multiple classes/types in a tuple format. For example, you can pass

   Yes

   5,

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

   5,

   Yes

   9,

   # 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

   0, or any user-created class.

3. Execute your operation, If result is True

   The

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

   2 returns True if an object or variable is of a specified type otherwise False.

Example

Using isintance() we can verify whether a variable is a number or string. Let’s assume variable

# 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

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

Output:

Yes

As we can see in the output, the

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

# 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

# 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 the

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

# 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

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

Yes

# 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

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

# 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

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

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

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

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

Yes

# 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

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

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

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

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

You can verify if the

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

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

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

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

# 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

The

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

The

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

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

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

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

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

• Checking if an object is of type

  Yes

  9 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

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

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.

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

Check if elements of a list are numbers or strings

Check each element’s type with multiple numeric types such as

Yes

# 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

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

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

How are variables initialized in Python?

How do you check variables in Python?

How do you check if a variable is undefined in Python?

How to check if environment variable exists in Python?