Variables & Data Types contains an exhaustive information about these concepts, this guide provides a Python specific reference.

Declaring Variables

One of the most basic things to do in a Python program is to declare a variable and set it equal to a value of some data type. We’ll talk more about data types later.

num_of_students = 10     # integer 
student_name = "James"   # string   
test_score = 5.4         # float
working_status = True    # boolean 

Types

Variables can store a number of different types of data in Python.

num_of_students = 10         # declare variable of type integer   
print(type(num_of_students)) # prints <class 'int'>

student_name = "James"       # declare variable of type string   
print(type(student_name))    # prints <class 'str'>

test_score = 5.4             # declare variable of type string  
print(type(test_score))      # prints <class 'float'>

working_status = True        # declare variable of type boolean  
print(type(working_status))  # prints <class 'bool'>

Dynamic Typing

Python is a dynamically typed language, meaning that the data/variable type is determined at run time. This also means that Python allows us to change the type of data assigned to a variable.

x = 1
print(type(x))         # prints <class 'int'>

x = "Hello World"
print(type(x))         # prints <class 'str'>

In general, this can get us into trouble when pass our variables and data through to different operations or functions that require specific types of data. Try executing the following code:

x = input("x: ")      # prompt user for keyboard input
y = x + 1             # throws error because x is a string

The following program will cause an error (or exception) in Python. Why is this?

+ is a mathematical operator that can only perform addition on integers or float data types.

input() is a Python function that outputs the string of characters entered by the user on the keyboard, in this case it was stored in a variable x.

Simply put, it does not make sense to add a string with an integer and so Python complains that we are trying to do something nonsensical in the program.

To fix this problem, we can perform a type conversion to convert the string to an integer.

Type Conversion

In Python, we can convert data from one type to another using the type casting operators.

x = input("x: ")      # prompt user for keyboard input
print(type(x))        # prints <class 'str'>

x = int(x)            # convert x to an integer
print(type(x))        # prints <class 'int'>

y = x + 1             # add 1 to x and assign the result to y

<aside> 🔥 Let’s refactor our code into a more efficient statement.

</aside>

x = int(input("x: ")
y = x + 1