Day 2: Comments and Printing Text/Numbers in Python

Introduction to Day 2

Welcome to Day 2 of our Python journey! Yesterday, you took your first steps into the world of programming. Today, we'll learn two fundamental concepts that are crucial for writing clear, readable, and interactive Python code: comments and the print() function. Comments help us understand our code, while print() allows our programs to display information to the user.

1. Understanding Comments in Python

1.1 What are Comments?

In programming, comments are lines of text within the code that are ignored by the Python interpreter. They are not executed as part of the program. Instead, they serve as notes or explanations for human readers.

1.2 Why Use Comments?

Comments are incredibly important for several reasons:

• Clarity: They explain what the code does, especially complex or non-obvious parts.
• Maintainability: When you (or someone else) revisit code after a long time, comments help recall the logic and purpose.
• Debugging: You can temporarily "comment out" lines of code to test different parts of your program without deleting them.
• Collaboration: In team projects, comments facilitate understanding among multiple developers.

1.3 Types of Comments in Python

1.3.1 Single-Line Comments (#)

The most common type of comment in Python starts with a hash symbol (#). Anything following # on that line is considered a comment and is ignored by the interpreter.

# This is a single-line comment.
# It explains the next line of code.
print("Hello, Python learners!") # This comment explains what the print statement does.

# You can also use comments to disable code temporarily:
# print("This line will not be executed.")

1.3.2 Multi-Line Comments (Docstrings / Triple Quotes)

Python does not have a specific multi-line comment syntax like some other languages. However, you can achieve multi-line comments by using triple quotes (''' or """). When these triple-quoted strings are not assigned to a variable, they act as comments. If placed immediately after a function, class, or module definition, they are known as "docstrings," which serve a specific documentation purpose.

"""
This is an example of a multi-line comment.
It spans across multiple lines.
This is often used for longer explanations or for
temporarily disabling large blocks of code.
"""
print("Learning about comments is fun!")

'''
Another way to write multi-line comments
using single triple quotes.
Both work the same way for this purpose.
'''
x = 10
print(x)

2. Printing Text and Numbers with print()

2.1 The print() Function

The print() function is one of the most fundamental functions in Python. It's used to display output to the console or terminal. This output can be text, numbers, or the values of variables.

2.2 Printing Plain Text (Strings)

To print text, you enclose the text within single quotes (' ') or double quotes (" "). This is called a "string".

print("Welcome to Day 2 of Python!")
print('Python is a versatile programming language.')
print("Don't forget to practice!")

2.3 Printing Numbers

You can also directly print numbers (integers or floating-point numbers) without quotes. Python will display their numerical value.

print(100)           # An integer
print(3.14159)       # A floating-point number
print(1 + 2 * 3)     # Python will calculate the expression first

2.4 Printing Variables

Once you've stored data in a variable, you can print the value of that variable by simply passing its name to the print() function.

message = "Hello, World!"
age = 25
temperature = 20.5

print(message)
print(age)
print(temperature)

2.5 Combining Text and Numbers in Print Statements

Often, you'll want to display text alongside numbers or variable values to make your output more informative. Python offers several ways to do this.

2.5.1 Using the Comma (,) for Separation

The easiest way to combine different types of data (strings, numbers, variables) in a single print() statement is to separate them with commas. By default, print() will insert a space between each item.

name = "Alice"
score = 98
print("Student:", name, "achieved a score of", score, "points.")

items_in_cart = 5
total_cost = 50.75
print("You have", items_in_cart, "items in your cart. Total:", total_cost)

2.5.2 Using the Plus Sign (+) for Concatenation (Strings Only)

The + operator can be used to "concatenate" (join) strings. However, it can *only* join strings with other strings. If you want to combine a number with a string using +, you must first convert the number to a string using the str() function.

first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print("Welcome, " + full_name + "!")

item_count = 3
# print("Total items: " + item_count) # This would cause a TypeError!
print("Total items: " + str(item_count)) # Correct way: convert number to string

2.5.3 Formatted String Literals (f-strings) - Recommended

Introduced in Python 3.6, f-strings provide a concise and readable way to embed expressions inside string literals. They are highly recommended for combining text and variables.

To use an f-string, you put an f or F before the opening quote of the string, and then you can embed expressions inside curly braces {} within the string.

product = "Laptop"
price = 1200.50
quantity = 2

print(f"You purchased {quantity} {product}(s) for a total of ${price * quantity}.")

city = "New York"
temp = 22
print(f"The temperature in {city} is {temp}°C.")

2.6 Advanced Print Function Arguments: sep and end

The print() function has optional arguments that allow you to control how items are separated and what happens at the end of the line.

2.6.1 The sep Argument

By default, the sep (separator) argument for print() is a single space (' '). You can change this to any string you like, which will be inserted between the items you print.

print("apple", "banana", "cherry")            # Default: separated by space
print("apple", "banana", "cherry", sep=", ")  # Separated by comma and space
print("Year", "Month", "Day", sep="-")        # Separated by hyphen
print("user", "example", "com", sep="@")      # Creating an email address

2.6.2 The end Argument

By default, print() adds a newline character (\n) at the end of its output, meaning the next print() statement will start on a new line. You can change this behavior using the end argument.

print("This is the first line.")
print("This is the second line.")

print("Hello", end=" ") # Notice the space at the end
print("World!")         # This will print on the same line as "Hello"

print("Loading", end="...")
print(" Done!")         # Both parts appear on one line: Loading... Done!

Conclusion

Today, we delved into two crucial aspects of Python programming: comments and the print() function. Comments are your way of making your code understandable to yourself and others, ensuring readability and maintainability. The print() function is your program's voice, allowing it to communicate results, messages, and variable values to the user. Mastering these concepts will empower you to write more expressive and user-friendly Python programs. Keep practicing, and we'll explore more exciting topics in the next session!