Python Tutorial: Print Output and Work with Variables

This tutorial will guide you through the fundamentals of printing output and working with variables in Python. We’ll build up our understanding through a series of examples, focusing on clear, concise code and explanations.

Example 1: Basic Printing and String Concatenation

The first step is to learn how to print text to the console. We’ll also explore how to combine strings using concatenation.

# This program prints a greeting message and calculates the area of a rectangle.

# Define variables
name = "Alice"
length = 5
width = 3

# Print the greeting
print("Hello, " + name + "!")

# Calculate the area
area = length  width

# Print the area
print("The area of the rectangle is: " + str(area))

In this example:

• We define variables `name`, `length`, and `width` with different values.
• We use the `print()` function to display text and the calculated area.
• The `str()` function is used to convert the numerical `area` value to a string before concatenating it with the other string parts. This is necessary because you cannot directly concatenate a number with a string in Python.

Let’s trace the execution:

1. `name` is assigned “Alice”.
2. `length` is assigned 5.
3. `width` is assigned 3.
4. `print(“Hello, ” + name + “!”)` prints “Hello, Alice!”.
5. `area = length width` calculates 5 3 = 15 and stores it in `area`.
6. `print(“The area of the rectangle is: ” + str(area))` prints “The area of the rectangle is: 15.”.

# This program demonstrates different ways to print output.

# Using f-strings (formatted string literals) - Recommended
print(f"My name is {name} and I am {age} years old.")

# Using the .format() method
print("My name is {} and I am {} years old.".format(name, age))

# Using the % operator (older style)
print("My name is %s and I am %d years old." % (name, age))

In this example, we show three ways to print output with formatted strings. F-strings are the most modern and readable, while the other two have their uses as well.

Let’s trace the execution:

1. We are using the f-string to print a personalized greeting.
2. We are using the .format() method to print a personalized greeting.
3. We are using the % operator to print a personalized greeting.

Example 2: Working with Numbers and Calculations

Now, let’s explore basic arithmetic operations and how to handle different data types like integers and floats. We’ll calculate the square of a number and perform addition and subtraction.

# This program calculates the square of a number and performs basic arithmetic operations.

# Define variables
number = 7

# Calculate the square
square = number  number

# Perform addition and subtraction
sum_result = 10 + 5
difference_result = 20 - 8

# Print the results
print("The square of", number, "is:", square)
print("10 + 5 =", sum_result)
print("20 - 8 =", difference_result)

# Experiment with floats
float_number = 3.14
float_sum = 2.5 + float_number
print("Sum of 2.5 and", float_number, "is:", float_sum)

Here, we demonstrate:

• Basic arithmetic operations (multiplication, addition, subtraction).
• How to handle integer and float data types.
• String formatting for clear output.

Let’s trace the execution:

1. `number` is assigned 7.
2. `square` is calculated as 7 7 = 49.
3. `sum_result` is calculated as 10 + 5 = 15.
4. `difference_result` is calculated as 20 – 8 = 12.
5. We print the results of the calculations.
6. We demonstrate the addition of a float (3.14) with a float (2.5).

Example 3: Input from the User (Simple Prompt)

Finally, let’s take input from the user using the `input()` function. We’ll ask the user for their name and print a personalized greeting.

# This program takes user input and prints a personalized greeting.

# Prompt the user to enter their name
name = input("Enter your name: ")

# Print a greeting
print("Hello, " + name + "!")

In this example:

• We use the `input()` function to prompt the user to enter their name.
• The `input()` function returns a string.
• We concatenate this string with “Hello, ” and “!” to create a personalized greeting.

Let’s trace the execution:

1. The program pauses and waits for the user to type their name and press Enter.
2. The user enters “Bob”.
3. `print(“Hello, ” + name + “!”)` prints “Hello, Bob!”.

# This program demonstrates input validation (basic example)

# Prompt the user for a number
try:
  number = int(input("Enter a positive integer: "))
  if number > 0:
    print("You entered:", number)
  else:
    print("Please enter a positive integer.")
except ValueError:
  print("Invalid input.  Please enter a valid integer.")

This example demonstrates basic input validation. This checks to see that the input entered by the user is a positive integer. If not, it throws an error. The try/except block allows the user to try to enter an integer, and the program doesn’t crash.

Output:

Output for Example 1:
Hello, Alice!
The area of the rectangle is: 15.

Output for Example 2:
The square of 7 is: 49
10 + 5 = 15
20 - 8 = 12
Sum of 2.5 and 3.14 is: 5.64

Output for Example 3:
Enter your name: Bob
Hello, Bob!

Output for Example 3 (with input validation):

Output for Example 3:
Enter a positive integer: 10
You entered: 10

Output for Example 3:
Enter a positive integer: -5
Please enter a positive integer.

Output for Example 3:
Enter a positive integer: abc
Invalid input.  Please enter a valid integer.