Comments & Input/Output Operations in Python

1. Comments in Python

Comments are non-executable explanatory notes written inside source code to make the program easier for humans to understand. The Python Interpreter completely ignores comments during execution.

In Python, comments are written in three ways:

1. Single-Line Comments (#)

Any text starting with a hash symbol (#) is treated as a single-line comment. It can be placed on its own line or inline at the end of a code statement:

# Calculate area of a circle
radius = 5
area = 3.14159 * (radius ** 2)  # Inline comment: ** is power operator

2. Multi-Line Comments

When you need to write a comment spanning several lines, you can either put # at the start of each line OR enclose the block inside triple quotes (''' ... ''' or """ ... """):

# Author  : CampusNotes Team
# Course  : BCA (DAVV Indore)
# Subject : Python Programming - Unit 1

3. Docstrings (Documentation Strings — """ ... """)

A Docstring is a special multi-line string literal enclosed in triple quotes (""" ... """) that appears as the very first statement inside a module, function, class, or method definition.

• Difference between a Comment and a Docstring: Unlike # comments (which are stripped out and ignored by Python), Docstrings are retained at runtime and can be inspected using function_name.__doc__ or help(function_name)!

def add_numbers(a, b):
    """This function takes two numbers and returns their sum."""
    return a + b

print(add_numbers.__doc__)
# Output: This function takes two numbers and returns their sum.

2. Input Operations in Python (input() Function)

To make a program interactive, we need to accept input from the user via the keyboard. Python provides the built-in input() function for this purpose.

Syntax of input():

variable_name = input("Prompt message displayed to user: ")

Golden Rule of input() in Python:

input() ALWAYS returns the user’s input as a String (str)! Even if the user types a number like 25 or 99.5, input() returns it as the string "25" or "99.5". Therefore, to perform mathematical calculations, you must explicitly type-cast input() using int(), float(), or eval()!

# 1. Reading a String input (No type-casting needed)
name = input("Enter your name: ")

# 2. Reading an Integer input using int(input())
age = int(input("Enter your age: "))

# 3. Reading a Float (decimal) input using float(input())
percentage = float(input("Enter your 12th percentage: "))

# 4. Reading MULTIPLE space-separated inputs on a single line using .split()
x, y = map(int, input("Enter two numbers separated by space: ").split())
print("Sum =", x + y)

3. Output Operations in Python (print() Function)

To display output on the console screen, Python provides the built-in print() function.

Complete Syntax of print():

print(value1, value2, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

Two Super-Important Parameters of print(): sep and end

This is a favorite 2-mark and 5-mark question in DAVV BCA exams!

1. sep (Separator Parameter — Default is a single space ' '): Specifies the character or string used to separate multiple values passed inside a single print() call.
2. end (End Parameter — Default is a newline '\n'): Specifies what character is printed at the very end of the print() statement. By default, print() moves to a new line (\n), but setting end=" " keeps the next print() on the same line!

# 1. Default print (sep=' ', end='\n')
print("BCA", "DAVV", "Indore")
# Output: BCA DAVV Indore

# 2. Using custom 'sep' parameter
print("02", "04", "2026", sep="-")
# Output: 02-04-2026

print("ishaan", "campusnotes.in", sep="@")
# Output: [email protected]

# 3. Using custom 'end' parameter to print on the SAME line
print("Hello", end=" ")
print("World!")
# Output: Hello World!

4. 3 Ways of Formatting Output in Python

When displaying variables mixed with text, Python offers three formatting styles (with f-strings being the cleanest modern standard):

Complete Program Demonstrating Input, Calculation & Formatted Output:

# Program to read student details and display a formatted marksheet
name = input("Enter Student Name: ")
roll = int(input("Enter Roll Number: "))
m1, m2, m3 = map(float, input("Enter marks of 3 subjects: ").split())

total = m1 + m2 + m3
percentage = total / 3

print("\n" + "=" * 35)
# Using f-string formatting (:.2f rounds float to 2 decimal places)
print(f"Student Name : {name}")
print(f"Roll Number  : {roll}")
print(f"Total Marks  : {total} / 300")
print(f"Percentage   : {percentage:.2f}%")
print("=" * 35)

Sample Run:

Enter Student Name: Ananya Sharma
Enter Roll Number: 105
Enter marks of 3 subjects: 85 90 88

===================================
Student Name : Ananya Sharma
Roll Number  : 105
Total Marks  : 263.0 / 300
Percentage   : 87.67%
===================================

💡 Exam Preparation Tips for DAVV BCA

• Always mention that input() returns a str by default, so int(input()) or float(input()) is required for numeric input!
• In any question on Output operations, always demonstrate the sep and end keyword arguments of print() along with f-strings (f"...").