Variables, Data Types, and I/O Basics

1. What are Variables?

Think of a variable as a labeled box where you can store a piece of information. In programming, we give these boxes names (called identifiers) and put values inside them. This allows us to refer to and manipulate data easily. Given your math background, this is very similar to how you use variables like $x$ or $y$ in algebra to represent unknown values in an equation.

To create a variable in Python, you simply choose a name, use the equals sign (=), and provide the value you want to store.

# Here, 'age' is the variable name and 25 is the value.
age = 25




# 'name' is the variable name and "Alice" is the value.
name = "Alice"

To get a quick introduction to this concept, let's watch a short video.

2. Basic Data Types

The "type" of data a variable holds determines what you can do with it. You can perform arithmetic with numbers, but not with text. Python has several built-in data types, but for now, we'll focus on the four most fundamental ones.

The same video you just started will now walk you through them.

Here is a summary of these data types for your reference:

• Integer (int): Represents whole numbers, positive or negative (e.g., 10, -3, 0).
• Float (float): Represents numbers with a decimal component (e.g., 98.6, -0.5, 3.14).
• String (str): Represents text. String values are always enclosed in single (') or double (") quotes (e.g., "Hello", 'Python').
• Boolean (bool): Represents one of two values: True or False. Note that the first letter is always capitalized. These are crucial for making decisions in your code.

This table provides a concise overview.

3. Interacting with the User: Input and Output

Programs are much more interesting when they can interact with a user. This is done through input (getting data from the user) and output (displaying data to the user).

Output with print()

You've already used print() to display "Hello, World!". You can also use it to display the value stored in a variable. It's often useful to mix text and variables to create meaningful messages. While there are a few ways to do this, the most modern and readable method is using f-strings.

An f-string is a string literal prefixed with the letter f that allows you to embed expressions, like variable names, directly inside curly braces {}.

Input with input() and the Importance of Type Conversion

To get data from a user, we use the input() function. This function displays a prompt to the user, waits for them to type something and press Enter, and then returns what they typed.

There's a critical rule to remember: input() always returns the data as a string.

This means if the user types the number 25, input() gives you the string "25", not the integer 25. If you want to perform math with that number, you first need to convert its data type.

• int(value) converts a value to an integer.
• float(value) converts a value to a float.
• str(value) converts a value to a string.

This process is called type casting or type conversion.

4. Hands-On Practice

Now it's time to write some code yourself. Open PyCharm (or your chosen editor) and try these exercises.

Exercise 1: Declare and Print

Create a new Python file (e.g., user_profile.py). In this file, write a program that does the following:

1. Create a variable name and assign it your name (as a string).
2. Create a variable age and assign it your age (as an integer).
3. Create a variable height_meters and assign it your height in meters (as a float).
4. Create a variable is_learning and set it to True (as a boolean).
5. Use print() with f-strings to display a summary, like:

   User Profile:
   Name: [Your Name]
   Age: [Your Age]
   Height: [Your Height] meters
   Currently learning Python: [True/False]
   

Solution:

name = "Alex"
age = 28
height_meters = 1.8
is_learning = True

print(f"User Profile:")
print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height_meters} meters")
print(f"Currently learning Python: {is_learning}")

Exercise 2: Area of a Rectangle

Create another Python file (e.g., rectangle_area.py). Write a program that calculates the area of a rectangle.

1. Use the input() function to ask the user for the length of the rectangle.
2. Use input() again to ask the user for the width of the rectangle.
3. Remember that input() returns strings. Convert both the length and width to floats using float().
4. Calculate the area (area = length * width).
5. Print the result in a user-friendly sentence, for example: "The area of the rectangle is [area] square units."

Solution:

print("Rectangle Area Calculator")




# Get input from the user
length_str = input("Enter the length of the rectangle: ")
width_str = input("Enter the width of the rectangle: ")




# Convert the string inputs to floats
length = float(length_str)
width = float(width_str)




# Calculate the area
area = length * width




# Print the result
print(f"The area of the rectangle is {area} square units.")

For more reading and examples, you can review the following article.

Conclusion

Excellent work! You have just learned the absolute fundamentals of how programs manage and process information. These concepts are the foundation upon which all complex algorithms are built.

Here are the key takeaways from today's lesson:

• Variables are named containers for storing data (name = "value").
• Python's core data types are int (whole numbers), float (decimal numbers), str (text), and bool (True/False).
• The print() function displays information, and f-strings are a powerful way to format output.
• The input() function gets data from the user, but always as a string.
• You must use type conversion functions like int() and float() to turn input strings into numbers before doing calculations.

In the next lesson, we will build directly on this by exploring the different kinds of operators in Python. You'll learn how to perform more complex arithmetic, compare values, and combine logical conditions—all essential skills for controlling how your programs run.