Session 3

🔄 Loops & Conditions

Control the flow of your Python programs

📚 10 Topics ⏱️ 60 min read 🎯 Essential Level

🗺️ What You'll Learn

🔀 Comparison Operators
🤔 if, elif, else Statements
🔁 for Loops
♾️ while Loops
🎯 range() Function
⏹️ break, continue, pass

📘 Same topic in the course notebook

Session_3 Loops and Conditions has the same ideas: if/elif/else, for, while, break, continue. Run the notebook cells to practice.

🚦

Think of It Like Driving!

🟢 if (green light) → Go!
🟡 elif (yellow light) → Slow down!
🔴 else (red light) → Stop!
🔄 Loop → Drive around the roundabout

Conditions check situations, loops repeat actions!

🔀 Comparison Operators

3.1

⚖️ Comparing Values

Comparison operators compare two values and return True or False. They're the foundation of decision-making in code!

🎯 All Comparison Operators

Operator Meaning Example Result
== Equal to 5 == 5 True
!= Not equal to 5 != 3 True
> Greater than 7 > 3 True
< Less than 2 < 5 True
>= Greater than or equal 5 >= 5 True
<= Less than or equal 3 <= 5 True
Python From Source 
# Comparison operators from Session 3
a = 10
b = 5

# Equal and not equal
print(a == b)   # False (10 is not equal to 5)
print(a != b)   # True (10 is not equal to 5)

# Greater and less than
print(a > b)    # True (10 is greater than 5)
print(a < b)    # False (10 is not less than 5)

# Greater/less than or equal
print(a >= 10)  # True (10 is equal to 10)
print(b <= 5)   # True (5 is equal to 5)
Output
False
True
True
False
True
True
⚠️ Common Mistake: = vs ==

= is for assignment: x = 5 (put 5 in x)

== is for comparison: x == 5 (is x equal to 5?)

🧠 Logical Operators

3.2

🔗 Combining Conditions

Logical operators let you combine multiple conditions together!

🎯 The Three Logical Operators

    AND 🤝  →  Both conditions must be True
              "I need coffee AND breakfast"
              
    OR 🤷   →  At least one condition must be True
              "I'll have tea OR coffee"
              
    NOT 🚫  →  Flips True to False, False to True
              "I do NOT want spam"
Python From Source 
# Logical operators from Session 3
age = 25
has_license = True
is_tired = False

# AND - Both must be True
can_drive = age >= 18 and has_license
print("Can drive:", can_drive)  # True

# OR - At least one must be True
needs_rest = is_tired or age > 60
print("Needs rest:", needs_rest)  # False

# NOT - Reverses the boolean
is_awake = not is_tired
print("Is awake:", is_awake)  # True

# Complex combinations
x = 15
print(x > 10 and x < 20)  # True (x is between 10 and 20)
print(x < 5 or x > 10)    # True (x is greater than 10)
Output
Can drive: True
Needs rest: False
Is awake: True
True
True

🤔 Conditional Statements (if/elif/else)

3.3

🚦 The if Statement

The if statement runs code only when a condition is True. It's like a guard at a door!

🚪 How IF Works

          START
            │
            ▼
    ┌───────────────┐
    │  Condition    │
    │   True?       │
    └───────┬───────┘
        Yes │ No
            ▼    ╲
    ┌───────────┐  ╲
    │ Run Code  │   │
    └───────────┘   │
            │      │
            ▼     ◀
          END
Python From Source 
# Simple if statement from Session 3
temperature = 35

if temperature > 30:
    print("It's hot outside! 🔥")
    print("Stay hydrated!")

# This code runs regardless of the condition
print("Have a nice day!")
Output
It's hot outside! 🔥
Stay hydrated!
Have a nice day!
💡 Indentation is Everything!

Python uses indentation (spaces/tabs) to group code. Everything indented after if belongs to that if block. Use 4 spaces consistently!

3.4

↔️ The if-else Statement

The else block runs when the if condition is False. It's the "otherwise" option!

🔀 The Fork in the Road

            Is it raining? 🌧️
                  │
         ┌───Yes─┴───No───┐
         ▼                ▼
    Take umbrella ☂️  Wear sunglasses 😎
Python From Source 
# if-else from Session 3
age = 16

if age >= 18:
    print("You can vote! 🗳️")
else:
    print("Sorry, you're too young to vote.")
    years_left = 18 - age
    print(f"Wait {years_left} more years.")
Output
Sorry, you're too young to vote.
Wait 2 more years.
3.5

🔢 The if-elif-else Chain

When you have multiple conditions to check, use elif (short for "else if"). Python checks each condition in order and runs the first one that's True!

🎢 The Decision Waterfall

    score = 85
         │
    ┌────▼────┐
    │ >= 90?  │──Yes──→ "A" 🌟
    └────┬────┘
         │ No
    ┌────▼────┐
    │ >= 80?  │──Yes──→ "B" ✨  ← (This runs!)
    └────┬────┘
         │ No
    ┌────▼────┐
    │ >= 70?  │──Yes──→ "C" 👍
    └────┬────┘
         │ No
         ▼
       "F" 😢
Python From Source 
# Grade calculator from Session 3
score = 85

if score >= 90:
    grade = "A"
    print("Excellent! 🌟")
elif score >= 80:
    grade = "B"
    print("Good job! ✨")
elif score >= 70:
    grade = "C"
    print("Not bad! 👍")
elif score >= 60:
    grade = "D"
    print("Need improvement 📚")
else:
    grade = "F"
    print("Please see the teacher 😢")

print(f"Your grade: {grade}")
Output
Good job! ✨
Your grade: B
3.6

🪆 Nested if Statements

You can put if statements inside other if statements - like Russian nesting dolls!

Python From Source 
# Nested if from Session 3
age = 25
has_ticket = True
is_vip = False

if age >= 18:
    print("Age verified ✓")
    if has_ticket:
        print("Ticket verified ✓")
        if is_vip:
            print("Welcome to the VIP section! 🌟")
        else:
            print("Welcome to the general section! 🎉")
    else:
        print("Please buy a ticket first 🎫")
else:
    print("Sorry, this event is for adults only 🔞")
Output
Age verified ✓
Ticket verified ✓
Welcome to the general section! 🎉

🔁 For Loops

3.7

🎠 Iterating Through Items

A for loop repeats code for each item in a sequence. Think of it like a assembly line in a factory - each item gets processed!

🏭 The For Loop Assembly Line

    Items: [🍎, 🍊, 🍋, 🍇]
           │   │   │   │
           ▼   ▼   ▼   ▼
         ┌─────────────┐
         │  Process    │  ← Same operation
         │  Each Item  │     on each item
         └─────────────┘
           │   │   │   │
           ▼   ▼   ▼   ▼
    Output: 🍎✓ 🍊✓ 🍋✓ 🍇✓
Python From Source 
# Basic for loop from Session 3
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(f"I love {fruit}s! 🍽️")
Output
I love apples! 🍽️
I love bananas! 🍽️
I love cherrys! 🍽️

🔤 Looping Through Strings

Python From Source 
# Loop through each character
word = "Python"

for letter in word:
    print(letter, end=" → ")
print("Done!")
Output
P → y → t → h → o → n → Done!
3.8

🎯 The range() Function

range() generates a sequence of numbers. It's perfect when you want to loop a specific number of times!

🔢 Understanding range()

    range(5)        → 0, 1, 2, 3, 4      (starts at 0, stops BEFORE 5)
    range(2, 6)     → 2, 3, 4, 5         (starts at 2, stops BEFORE 6)
    range(0, 10, 2) → 0, 2, 4, 6, 8      (step by 2)
    range(5, 0, -1) → 5, 4, 3, 2, 1      (countdown!)
    
    🎯 Remember: The end number is NOT included!
Python From Source 
# range() examples from Session 3

# Basic range - prints 0 to 4
print("range(5):")
for i in range(5):
    print(i, end=" ")
print()

# Range with start and end
print("range(2, 7):")
for i in range(2, 7):
    print(i, end=" ")
print()

# Range with step
print("range(0, 10, 2) - even numbers:")
for i in range(0, 10, 2):
    print(i, end=" ")
print()

# Countdown
print("Countdown:")
for i in range(5, 0, -1):
    print(i, end="... ")
print("Blast off! 🚀")
Output
range(5):
0 1 2 3 4 
range(2, 7):
2 3 4 5 6 
range(0, 10, 2) - even numbers:
0 2 4 6 8 
Countdown:
5... 4... 3... 2... 1... Blast off! 🚀

📊 Practical Example: Sum of Numbers

Python From Source 
# Calculate sum of 1 to 10
total = 0

for num in range(1, 11):  # 1 to 10
    total = total + num
    print(f"Added {num}, total is now {total}")

print(f"\\nFinal sum: {total}")
Output
Added 1, total is now 1
Added 2, total is now 3
Added 3, total is now 6
...
Final sum: 55

♾️ While Loops

3.9

🔄 Repeat While Condition is True

A while loop keeps running as long as a condition is True. It's like saying "keep doing this until..."

🎡 The While Loop Ferris Wheel

             ┌─────────────────┐
             │  Is condition   │◄─────┐
             │     True?       │      │
             └────────┬────────┘      │
                      │               │
              Yes     │     No        │
                      ▼               │
             ┌─────────────────┐      │
             │   Run the code  │──────┘
             └─────────────────┘
                      │
                      │ No
                      ▼
                    EXIT
Python From Source 
# Basic while loop from Session 3
count = 1

while count <= 5:
    print(f"Count is: {count}")
    count = count + 1  # IMPORTANT: Update the condition!

print("Loop finished!")
Output
Count is: 1
Count is: 2
Count is: 3
Count is: 4
Count is: 5
Loop finished!
⚠️ Beware of Infinite Loops!

Always make sure your condition will eventually become False, otherwise your program will run forever!

while True: # This runs FOREVER! ♾️

🎮 Practical Example: Guessing Game

Python From Source 
# Simulated guessing game from Session 3
secret = 7
guess = 0
attempts = 0
guesses = [3, 5, 7]  # Simulated user guesses

while guess != secret:
    guess = guesses[attempts]
    attempts = attempts + 1
    
    if guess < secret:
        print(f"Guess {guess}: Too low! ⬆️")
    elif guess > secret:
        print(f"Guess {guess}: Too high! ⬇️")

print(f"🎉 Correct! The number was {secret}")
print(f"You got it in {attempts} attempts!")
Output
Guess 3: Too low! ⬆️
Guess 5: Too low! ⬆️
🎉 Correct! The number was 7
You got it in 3 attempts!

⏹️ Loop Control Statements

3.10

🛑 break, continue, and pass

These special keywords give you more control over how loops behave!

🎮 Loop Control Remote

    🛑 break    → STOP the loop completely
                  (Emergency exit!)
    
    ⏭️ continue → SKIP to next iteration
                  (Skip this one, do the next)
    
    ⏸️ pass     → Do NOTHING
                  (Placeholder, move along)

🛑 The break Statement

Python From Source 
# break example from Session 3
# Find the first number divisible by both 3 and 7
for num in range(1, 100):
    if num % 3 == 0 and num % 7 == 0:
        print(f"Found it: {num}")
        break  # Exit the loop immediately
    print(f"Checking {num}...")

print("Search complete!")
Output
Checking 1...
Checking 2...
...
Checking 20...
Found it: 21
Search complete!

⏭️ The continue Statement

Python From Source 
# continue example from Session 3
# Print only odd numbers
print("Odd numbers from 1-10:")
for num in range(1, 11):
    if num % 2 == 0:  # If even
        continue  # Skip this iteration
    print(num, end=" ")
Output
Odd numbers from 1-10:
1 3 5 7 9

⏸️ The pass Statement

Python From Source 
# pass example from Session 3
# Use pass as a placeholder
for i in range(5):
    if i == 2:
        pass  # TODO: Handle this case later
    else:
        print(f"Processing {i}")

# pass is useful for empty functions too
def future_feature():
    pass  # Will implement later
Output
Processing 0
Processing 1
Processing 3
Processing 4

🪆 Nested Loops

3.11

🔄🔄 Loops Inside Loops

You can put a loop inside another loop! The inner loop runs completely for each iteration of the outer loop.

📦 Nested Loops = Rows and Columns

    Outer loop (rows):    i = 1, 2, 3
                               │
         ┌─────────────────────┼─────────────────────┐
         │                     │                     │
         ▼                     ▼                     ▼
    Inner loop:           j = 1,2,3             j = 1,2,3
    (columns)             for i=1               for i=2
    
    Result:  (1,1) (1,2) (1,3)  →  (2,1) (2,2) (2,3)  → ...
Python From Source 
# Nested loops from Session 3
# Multiplication table
for i in range(1, 4):  # Outer loop: 1, 2, 3
    for j in range(1, 4):  # Inner loop: 1, 2, 3
        product = i * j
        print(f"{i} × {j} = {product}", end="\\t")
    print()  # New line after each row
Output
1 × 1 = 1	1 × 2 = 2	1 × 3 = 3	
2 × 1 = 2	2 × 2 = 4	2 × 3 = 6	
3 × 1 = 3	3 × 2 = 6	3 × 3 = 9

⭐ Creating a Pattern

Python From Source 
# Star pattern from Session 3
rows = 5

for i in range(1, rows + 1):
    for j in range(i):
        print("⭐", end="")
    print()  # New line
Output
⭐
⭐⭐
⭐⭐⭐
⭐⭐⭐⭐
⭐⭐⭐⭐⭐

🎯 Practical Examples

3.12

💼 Real-World Applications

🔢 FizzBuzz Challenge

Python From Source 
# Classic FizzBuzz from Session 3
for num in range(1, 16):
    if num % 3 == 0 and num % 5 == 0:
        print("FizzBuzz")
    elif num % 3 == 0:
        print("Fizz")
    elif num % 5 == 0:
        print("Buzz")
    else:
        print(num)

🔍 Finding Prime Numbers

Python From Source 
# Check for prime numbers from Session 3
for num in range(2, 20):
    is_prime = True
    
    for divisor in range(2, num):
        if num % divisor == 0:
            is_prime = False
            break
    
    if is_prime:
        print(f"{num} is prime! ⭐")
Output
2 is prime! ⭐
3 is prime! ⭐
5 is prime! ⭐
7 is prime! ⭐
11 is prime! ⭐
13 is prime! ⭐
17 is prime! ⭐
19 is prime! ⭐

🚫 Common Mistakes (Loops & Conditions)

💭 Short reflection

In one sentence: when would you choose a while loop instead of a for loop?

✅ CORE (Must know)

📚 NON-CORE (Good to know)

📋 Session Summary

Concept Syntax Use When
if if condition: Run code only if condition is True
elif elif condition: Check another condition if previous was False
else else: Run if all previous conditions are False
for for item in sequence: Iterate through each item
while while condition: Repeat until condition becomes False
range() range(start, stop, step) Generate number sequences
break break Exit loop immediately
continue continue Skip to next iteration

Complete code from course notebook: 3_loops_and_conditions_(1) (1).ipynb

Every line of code from the course notebook (verbatim).

# --- Code cell 1 ---
---last session
1.data types--numerical data types
2.Type casting

# --- Code cell 5 ---
11//3

# --- Code cell 6 ---
11%3

# --- Code cell 7 ---
4**3

# --- Code cell 8 ---
# '**'	: Exponentiation/power	→ 2 ** 3	= 8

# --- Code cell 9 ---
56/3

# --- Code cell 10 ---
56//3

# --- Code cell 11 ---
d=344%33
d

# --- Code cell 12 ---
3**4

# --- Code cell 13 ---
# Boolean data types are just True or False

# --- Code cell 15 ---
a==5

# --- Code cell 16 ---
#=  ------is assiging a value
#== ------to equal a value

# --- Code cell 17 ---
t=4

# --- Code cell 18 ---
3!=t

# --- Code cell 19 ---
t>=4

# --- Code cell 21 ---
a=12
a=a+6    #a+=6
a

# --- Code cell 22 ---
t=23
t*=2   # t=t*2
t

# --- Code cell 23 ---
r=56
r-=30  #r=r-30
r

# --- Code cell 25 ---
(55>31) & (100>14)  # and

# --- Code cell 26 ---
(55>31) | (10>14)   # or

# --- Code cell 27 ---
not (5>50)

# --- Code cell 28 ---
x=True
y=False
print(not y)     # not

# --- Code cell 29 ---
(5 > 10)

# --- Code cell 31 ---
# Example 1: Using 'is'
x = [1, 2, 3]
y = [3,4,5]
z = y

print(x is y)  # True — y refers to the same object as x
print(y is z)  # False — z has the same content, but is a different object

# Example 2: Using 'is not'
#print(x is not z)  # True

# --- Code cell 32 ---
id(x)

# --- Code cell 33 ---
id(y)

# --- Code cell 34 ---
id(z)

# --- Code cell 36 ---
d=[3,4,5,6]
3  not in d

# --- Code cell 37 ---
d.index(6)

# --- Code cell 41 ---
if condition:
  Block of code          # space called as indendation

# --- Code cell 42 ---
x = 1
if x > 5:
  print("x is greater than 5")

# --- Code cell 44 ---
x = 3
if x > 5:
  print("x is greater than 5")
else:
  print("x is not greater than 5")

# --- Code cell 46 ---
x =3

if x > 5:
  print("x is greater than 5")
elif x == 5:
    print("x is equal to 5")
else:
    print("x is less than 5")

# --- Code cell 47 ---
x = 283
y = 410

if x > y: # False
  print("b is greater than a")

else:
    print("anything")

# --- Code cell 48 ---
x = 2835
y = 283
if x == y: # True
    x = x + 1
    print(x)

else:
    print("anything")

# --- Code cell 50 ---
#indentation

x = 283
y = 410

if x > y:#False
    print("b is greater than a")

# --- Code cell 51 ---
x = 601
y = 610

if x > y:
  print("x is greater than y")
elif x == y:
  print("x is equal to y")
else:
  print("y is greater than x")

# --- Code cell 53 ---
x = 136
y = 228
z = 532

if z > y & y > x:
  print("Both conditions are True. x is smallest number")
else:
  print("anything")

# --- Code cell 54 ---
x = 136
y = 228
z = 132

if ( z > y and y > x ) | z>x:  # You can add brackets for deciding order of execution
  print("Both conditions are True. x is smallest number")
  x = x + 1
  print(x)

# --- Code cell 56 ---
x = 136
y = 228
z = 532

if z > y and y > x and z>x:  # Multiple conditions
  print("All conditions are True. x is smallest number")

# --- Code cell 57 ---
x = 136
y = 228
z = 532

if z < y or y < x:# False
  print("Atleast one condition is True")

# --- Code cell 58 ---
x = 136
y = 228
z = 532

if (z > y or y < x) and z>=x:
  print("Both condition are True")

# --- Code cell 59 ---
x = 136
y = 228
z = 532

if z > y or y < x and z>=x:  # order of conditions is important - left to right execution
  print("Both condition are True")

# --- Code cell 60 ---
x = 136
y = 228
z = 532

if z > y and y < x or z<=x:  # order of conditions is important - left to right execution
  print("Both condition are True")

# --- Code cell 61 ---
x = 1366
y = 228

if not x > y: # x<y
  print("x is NOT greater than y")

# --- Code cell 64 ---
x = 136
y = 228

if not x > y: #any condition

# --- Code cell 65 ---
x = 136
y = 228

if not x > y: #any condition
   pass       # PASS wont work in capitals

# --- Code cell 68 ---
for variable in iterable:
  block of code

# --- Code cell 69 ---
name="aravind"
for i in range(10):
  print(name)

# --- Code cell 70 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100,111]

for x in student_marks:
    print(x)

# --- Code cell 71 ---
college_name = "New College Name!"

for aravind in college_name:
  print(aravind)

# --- Code cell 72 ---
college_name = "New College Name"
college_name[3]

# --- Code cell 75 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

for z in student_marks:
    print(z)
    if(z==99):
        print('loop broke at z=', z)
        break

# --- Code cell 77 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

for z in student_marks:

    if(z>90):
        print("hello")
        continue


    print(z)

# --- Code cell 78 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

for z in student_marks:

    if(z>90):
        pass


    print(z)

# --- Code cell 79 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

for z in student_marks:

    if(z<120):
        break

    print(z)

# --- Code cell 82 ---
list(range(0,12,1))

# --- Code cell 83 ---
for k in range(10):
    print(k)

# --- Code cell 84 ---
## range(start_number, end_number, increment_size)
for k in range(0,21,2):
    print(k)

# --- Code cell 85 ---

#nested loops

# --- Code cell 86 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]
number = [1,2,3,4,5]

for i in student_marks:
  for j in number:
    print(i, j)

# --- Code cell 87 ---
data = [1, 2, 3, 4, 2.5]
# write a code such that it prints values less than 3

# --- Code cell 88 ---
for i in data:
    if (i<3):
        print(i)

# --- Code cell 89 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]
len(student_marks)

# --- Code cell 90 ---
range(8)

# --- Code cell 91 ---


for i in range(len(student_marks)):
    print(i)
    print(student_marks[i])

# --- Code cell 92 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]
number = [1,2,3,4,5]

for i in range(len(student_marks)):
  for j in range(len(number)):
    print(student_marks[i], number[j])

# --- Code cell 93 ---
len(student_marks)

# --- Code cell 94 ---
for x in student_marks:

# --- Code cell 95 ---

for x in student_marks:
    pass

# --- Code cell 97 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

# --- Code cell 98 ---
student_marks[0]

# --- Code cell 99 ---
len(student_marks)

# --- Code cell 100 ---


student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

i = 1
while i < len(student_marks):
  print(student_marks[i])
  i = i+1

# --- Code cell 101 ---
count =6 # initalize a variable

while count <= 10: #conditional check
    print(count)
    count += 1  # increase count by 1 each time

# --- Code cell 102 ---
len(student_marks)

# --- Code cell 103 ---
student_marks = [85, 88, 67, 65, 88, 99, 49, 100]

i = 0
while i < 4:
  print(student_marks[i])
  print("value of i", i)
  i = i+1