Python isinstance()

Understanding Python isinstance() Function

The isinstance() function in Python is a built-in function that checks if an object is an instance of a particular class or type. This is crucial for type checking and ensuring that your code works with the kinds of objects it expects. You provide the object, and the class (or a tuple of classes) and Python isinstance() returns True or False. It also considers inheritance.

Syntax of Python isinstance()

result = isinstance(object, classinfo)

Explanation

• result: Variable stores boolean which isinstance return.
• isinstance(): Built-in function for type checking.
• object: Object you’re checking.
• classinfo: Class, type, or tuple of classes/types.

Example of Python isinstance()

my_number = 5
is_int = isinstance(my_number, int)
print(is_int)

Explanation

• my_number = 5: Assigns integer 5 to a variable.
• is_int = isinstance(my_number, int): Checks my_number is instance of int.
• print(is_int): Prints returned value.

Output

True

isinstance() Parameters

The isinstance() function takes two parameters. The first parameter is the object you want to check. The second parameter, classinfo, specifies the type, class, or a tuple of types and/or classes you’re checking against. If you provide a tuple for the second parameter, Python isinstance() returns True if the object is an instance of any of the types or classes in that tuple. Otherwise, the function will return False.

Syntax

boolean_result = isinstance(object_to_check, type_or_class_or_tuple)

Explanation

• boolean_result: Stores True or False.
• isinstance(): Checks the object’s type.
• object_to_check: The object.
• type_or_class_or_tuple: Single type/class, or tuple of types/classes.

Example

my_string = "hello"
result = isinstance(my_string, (str, int))
print(result)

Explanation

• my_string = "hello": String variable.
• result = isinstance(my_string, (str, int)): Checks if string is an instance of either str or int.
• print(result): Prints the returned value.

Output

True

isinstance() Return Value

Python isinstance() function provides a boolean value: True or False. It returns True if the provided object is an instance of the specified class or type (or one of the classes/types if a tuple is provided). If the object is not an instance of any specified types or classes, it returns False. It also considers inheritance.

Syntax

true_or_false = isinstance(some_object, some_class)

Explanation

• true_or_false: Holds the boolean result.
• isinstance(): Performs the instance check.
• some_object: Object you want to check.
• some_class: Class, type, or tuple of classes/types.

Example

my_list = [1, 2, 3]
is_list = isinstance(my_list, list)
print(is_list)

Explanation

• my_list = [1, 2, 3]: List variable.
• is_list = isinstance(my_list, list): Checks my_list is instance of list.
• print(is_list): Displays output.

Output

True

Native Types with Python isinstance()

A common use of Python isinstance() is checking against Python’s native data types. You can verify if a variable holds a string, integer, float, list, dictionary, or any other built-in type. This allows you to write code that handles different data types differently. If your function expects a list, you can use isinstance() to ensure the provided argument is a list before your code attempts list-specific operations.

Syntax

check_result = isinstance(variable, native_type)

Explanation

• check_result: Will store boolean.
• isinstance(): Checks for type.
• variable: Object which type to be checked.
• native_type: Built-in type like int, str, list, dict, float.

Example

data = 10.5
is_float = isinstance(data, float)
print(is_float)

Explanation

• data = 10.5: Assigns floating value.
• is_float = isinstance(data, float): Check data is instance of float.
• print(is_float): Prints result.

Output

True

Int and List with Python isinstance()

Combining checks for int and list with Python isinstance() allows you to handle cases where you might accept either type. You can provide a tuple containing both int and list as the second argument to isinstance(). This flexibility lets you create more adaptable functions that can process individual integers or entire lists of integers, depending on what’s provided.

Syntax

is_int_or_list = isinstance(input_data, (int, list))

Explanation

• is_int_or_list: Stores boolean result.
• isinstance(): Performs check.
• input_data: Object which type to be checked.
• (int, list): Checks instance of either int or list.

Example

value = 25
result = isinstance(value, (int, list))
print(result)

Explanation

• value = 25: Assigns integer value.
• result = isinstance(value, (int, list)): Checks the value is instance of int or list.
• print(result): Prints the returned value.

Output

True

Objects with Python isinstance()

When working with object-oriented programming in Python, isinstance() is your go-to tool for verifying object types. You can check if an object is an instance of a specific class you’ve defined. It also checks for an inheritance; if you have a class hierarchy, Python isinstance() will return True if the object is an instance of the specified class or any of its parent classes.

Syntax

is_instance = isinstance(my_object, MyClass)

Explanation

• is_instance: Holds the True or False outcome.
• isinstance(): Built-in function for type checking.
• my_object: Object you’re checking.
• MyClass: The class.

Example

class Animal:
    pass

class Dog(Animal):
    pass

my_dog = Dog()
result = isinstance(my_dog, Animal)
print(result)

Explanation

• class Animal:: Defines base class.
• class Dog(Animal):: Dog class inherits from Animal.
• my_dog = Dog(): Creates an object.
• result = isinstance(my_dog, Animal): Checks object is instance of the class.
• print(result): Displays True because of inheritance.

Output

True

String with Python isinstance()

Checking if a variable holds a string is very common, and Python isinstance() makes it simple. You would use str as the second argument to isinstance(). This is crucial for data validation, ensuring a function receives string input before attempting string operations.

Syntax

is_string = isinstance(variable,str)

Explanation

• is_string: Stores returned value.
• isinstance(): Function to check if instance of a class.
• variable: Which is needed to be checked.
• str: Built-in type.

Example

text = "Sample string"
result = isinstance(text, str)
print(result)

Explanation

• text: Variable of string type.
• result: Stores the boolean result of isinstance(text, str).
• print(result): Outputs True.

Output

True

Dictionary with Python isinstance()

Using isinstance() to identify dictionaries is similar to how you use it to check other datatypes. Pass in the variable and dict class as the second parameter. The method will return True if the variable is an instance of dict; otherwise, it returns False.

Syntax

is_dictionary = isinstance(variable,dict)

Explanation

• is_dictionary: Holds return value.
• isinstance(): Checks the variable for dictionary type.
• variable: Represents data which is needed to be checked.
• dict: Keyword for dictionary.

Example

data = {"name": "Alice", "age": 30}
check = isinstance(data, dict)
print(check)

Explanation

• data: Defined dictionary.
• check = isinstance(data, dict): Verifies if data is a dictionary.
• print(check): Output the result (True).

Output

True

Class Methods with Python isinstance()

Within a class, you might have methods that need to behave differently depending on the type of object they receive as input. Python isinstance() is used inside a method to check the type of an argument. This is a form of conditional logic, You can tailor the method’s behavior based on whether it’s dealing with, say, a string, a list, or an instance of another class.

Syntax

class MyClass:
    def process_data(self, data):
        if isinstance(data, SomeType):
            # Do something specific to SomeType
            pass

Explanation

• class MyClass:: Declares class.
• def process_data(self, data):: Method which takes input data.
• if isinstance(data, SomeType):: Checks type of the object passed as a parameter.
• pass: Placeholder for specific handling.

Example

class Processor:
    def process(self, item):
        if isinstance(item, str):
            print("Processing string:", item.upper())
        elif isinstance(item, int):
            print("Processing integer:", item * 2)

processor = Processor()
processor.process("hello")
processor.process(5)

Explanation

• class Processor:: Defines Processor class.
• def process(self, item):: process method that takes parameter.
• if isinstance(item, str):: Checks if item is a string.
• print("Processing string:", item.upper()): If string, converts to uppercase and prints.
• elif isinstance(item, int):: Checks if item is integer.
• print("Processing integer:", item * 2): If it is integer, multiply by 2 and prints.
• processor = Processor(): Creates instance of class.
• processor.process("hello"): Calls process with string.
• processor.process(5): Calls process with integer.

Output

Processing string: HELLO
Processing integer: 10

Difference between isinstance() and type() Methods in Python

Both isinstance() and type() can be used to check a variable’s type. type() returns the exact type of an object, while isinstance() checks if an object is an instance of a class or its parent classes. Therefore, isinstance() is generally preferred because it handles inheritance correctly. Use type() only when you need to check for the exact type, not any subclasses.

Syntax

# isinstance() – Preferred for most cases
isinstance(object, class_or_type)

# type() – For strict type equality
type(object) is ExactType

Explanation

• isinstance(object, class_or_type): Checks inheritance.
• type(object) is ExactType: Checks for exact type match, not considering inheritance.

Example

class Parent:
    pass

class Child(Parent):
    pass

obj = Child()

print(isinstance(obj, Parent))  # Using isinstance()
print(type(obj) is Parent)    # Using type()

Explanation

• class Parent:: Defines class.
• class Child(Parent):: Inherits from Parent.
• obj = Child(): Creates a Child object.
• print(isinstance(obj, Parent)): Checks instance considering inheritance.
• print(type(obj) is Parent): Checks for exact type match.

Output

True
False

Conclusion

Python isinstance() is a built-in function in Python. It takes two parameters: the object and class info. Python isinstance returns True if the object is an instance of the provided class info; otherwise, it returns False. It is better to use isinstance() than type() as isinstance() considers inheritance.

Also Read

Python id()

Python int()

Python Reference

Python isinstance()