Since Python is a dynamically typed language we can declare a variable or the parameter of a function without having to declare their type. Python allows us to use something called annotations, which lets us specify the data type of a variable or the parameter of a function if we want to.

Examples

Without annotations

x = 3

def add(a, b):
    return a + b

With annotations

x: int = 3

def add(a: int, b: int) -> int:
    return a + b

NOTE: -> int means that the function will return an integer.

Since annotations are ignored by Python, we use a package called mypy. This package will check the code automatically for any type errors while coding.