How Do You Specify Data Type in Python?


Scott Campbell

Python is a dynamically typed language, which means that variables do not have an inherent data type. Instead, the data type of a variable is determined by the value assigned to it. However, there may be times when you want to explicitly specify the data type of a variable in Python.

Specifying Data Types

To specify the data type of a variable in Python, you can use what is known as type hinting. Type hinting allows you to provide additional information about the expected data type of a variable or function parameter.

Basic Data Types

Python has several built-in basic data types that you can use to specify the data type of a variable:

  • int: Used to store integer values.
  • float: Used to store floating-point values.
  • bool: Used to store boolean values (True or False).
  • str: Used to store string values.

For example, if you want to specify that a variable should be an integer, you can use the int keyword:

x: int = 5

This tells Python that the variable x should always contain an integer value.


Python also provides built-in collection types that allow you to specify the data type of multiple values:

  • List: Used to store multiple values in an ordered sequence.
  • Tuple: Similar to lists but are immutable (cannot be modified).
  • Set: Used to store unique values in an unordered collection.
  • Dictionary: Used to store key-value pairs.

To specify the data type of a collection, you can use square brackets and specify the data type inside:

numbers: List[int] = [1, 2, 3, 4]
person: Dict[str, Any] = {"name": "John", "age": 25}

In the above example, the variable ‘numbers’ is specified as a list that can only contain integer values. The variable ‘person’ is specified as a dictionary with string keys and any value type.

User-defined Types

In addition to the built-in data types, you can also create your own custom data types using classes in Python. Using these user-defined types allows you to specify your own data structures and their associated behaviors.

To define a user-defined type, you can create a class and define its attributes and methods:

class Person:
    def __init__(self, name: str, age: int): = name
        self.age = age

p1: Person = Person("John", 25)

In the above example, we define a class called ‘Person’ with attributes ‘name’ and ‘age’. We then create an instance of this class and assign it to the variable ‘p1’.

Type Checking Tools

Python provides several tools that allow you to perform type checking on your code:

  • mypy: A static type checker that can be used to analyze Python code for potential type errors.
  • pylint: A linter that checks for coding standards and potential errors in Python code.
  • pyright: A static type checker specifically designed for Python code in Visual Studio Code.

Using these tools, you can catch potential type errors early in the development process and ensure that your code is more robust and maintainable.


In Python, you can use type hinting to specify the data type of a variable. This allows you to provide additional information about the expected data type of a variable or function parameter.

Whether it’s basic data types, collections, or user-defined types, specifying the data type can help improve the clarity and maintainability of your code. Additionally, using type checking tools like mypy and pylint can further enhance the reliability of your codebase.

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