Python - Nested Loops
Hello, aspiring programmers! Today, we're going to dive into the fascinating world of nested loops in Python. As your friendly neighborhood computer teacher, I'm excited to guide you through this journey. Trust me, by the end of this lesson, you'll be looping like a pro!
What are Nested Loops?
Before we jump into the deep end, let's start with the basics. Imagine you're organizing your closet. You go through each shelf (that's one loop), and for each shelf, you sort through all the items on it (that's another loop inside the first one). That's essentially what nested loops are in programming – loops within loops!
Python Nested for Loop
Let's start with the for loop, which is like a reliable old friend in the Python world.
Basic Structure
Here's the general structure of a nested for loop:
for outer_variable in outer_sequence:
# Outer loop body
for inner_variable in inner_sequence:
# Inner loop bodySimple Example: Multiplication Table
Let's create a simple multiplication table to understand this better:
for i in range(1, 6):
for j in range(1, 6):
print(f"{i} x {j} = {i*j}", end="\t")
print() # Move to the next line after each rowThis code will output:
1 x 1 = 1 1 x 2 = 2 1 x 3 = 3 1 x 4 = 4 1 x 5 = 5
2 x 1 = 2 2 x 2 = 4 2 x 3 = 6 2 x 4 = 8 2 x 5 = 10
3 x 1 = 3 3 x 2 = 6 3 x 3 = 9 3 x 4 = 12 3 x 5 = 15
4 x 1 = 4 4 x 2 = 8 4 x 3 = 12 4 x 4 = 16 4 x 5 = 20
5 x 1 = 5 5 x 2 = 10 5 x 3 = 15 5 x 4 = 20 5 x 5 = 25 Let's break this down:
- The outer loop (
for i in range(1, 6)) runs 5 times, representing the rows. - For each iteration of the outer loop, the inner loop (
for j in range(1, 6)) runs 5 times, representing the columns. - We print each multiplication result, using
end="\t"to add a tab space instead of a new line. - After each row (outer loop iteration), we print an empty line to move to the next row.
Real-world Example: Seating Arrangement
Imagine you're a teacher (like me!) arranging seats for a class. Let's create a seating chart:
students = ["Alice", "Bob", "Charlie", "David", "Eve"]
rows = 3
seats_per_row = 2
seat_number = 0
for row in range(1, rows + 1):
print(f"Row {row}:")
for seat in range(1, seats_per_row + 1):
if seat_number < len(students):
print(f" Seat {seat}: {students[seat_number]}")
seat_number += 1
else:
print(f" Seat {seat}: Empty")
print() # Empty line between rowsThis will output:
Row 1:
Seat 1: Alice
Seat 2: Bob
Row 2:
Seat 1: Charlie
Seat 2: David
Row 3:
Seat 1: Eve
Seat 2: EmptyIn this example:
- The outer loop iterates through each row.
- The inner loop assigns students to seats in each row.
- We use a
seat_numbervariable to keep track of which student we're assigning next. - If we run out of students, we mark the remaining seats as "Empty".
Python Nested while Loop
Now, let's meet the while loop's cousin – the nested while loop. It's like a watchful guard that keeps checking a condition.
Basic Structure
Here's how a nested while loop typically looks:
while outer_condition:
# Outer loop body
while inner_condition:
# Inner loop bodyExample: Number Pyramid
Let's create a number pyramid to see nested while loops in action:
row = 1
while row <= 5:
col = 1
while col <= row:
print(col, end=" ")
col += 1
print() # Move to the next line
row += 1This will output:
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5 Let's break it down:
- The outer
whileloop controls the number of rows (1 to 5). - For each row, the inner
whileloop prints numbers from 1 to the current row number. - We increment
colinside the inner loop androwinside the outer loop.
Real-world Example: Inventory Check
Imagine you're managing a small store. You need to check your inventory regularly. Let's simulate this with nested while loops:
inventory = {
"apples": 50,
"bananas": 30,
"oranges": 40
}
days = 1
while days <= 3: # Check for 3 days
print(f"Day {days} Inventory Check:")
for fruit, quantity in inventory.items():
while quantity > 0:
print(f"Checking {fruit}...")
quantity -= 10 # Simulate selling 10 units each check
if quantity <= 20:
print(f"Low stock alert for {fruit}! Only {quantity} left.")
break # Stop checking this fruit if stock is low
inventory[fruit] = quantity # Update inventory
print(f"End of Day {days} Inventory: {inventory}\n")
days += 1This will output something like:
Day 1 Inventory Check:
Checking apples...
Checking apples...
Checking apples...
Low stock alert for apples! Only 20 left.
Checking bananas...
Low stock alert for bananas! Only 20 left.
Checking oranges...
Checking oranges...
Low stock alert for oranges! Only 20 left.
End of Day 1 Inventory: {'apples': 20, 'bananas': 20, 'oranges': 20}
Day 2 Inventory Check:
Checking apples...
Low stock alert for apples! Only 10 left.
Checking bananas...
Low stock alert for bananas! Only 10 left.
Checking oranges...
Low stock alert for oranges! Only 10 left.
End of Day 2 Inventory: {'apples': 10, 'bananas': 10, 'oranges': 10}
Day 3 Inventory Check:
Checking apples...
Low stock alert for apples! Only 0 left.
Checking bananas...
Low stock alert for bananas! Only 0 left.
Checking oranges...
Low stock alert for oranges! Only 0 left.
End of Day 3 Inventory: {'apples': 0, 'bananas': 0, 'oranges': 0}In this example:
- The outer
whileloop simulates checking inventory for 3 days. - We use a
forloop to iterate through each fruit in the inventory. - The inner
whileloop simulates checking and selling each fruit until it's low in stock or sold out. - We use
breakto stop checking a fruit if its quantity drops to 20 or below.
Conclusion
Congratulations! You've just mastered the art of nested loops in Python. Remember, nested loops are powerful tools, but use them wisely. They can make your code run slower if not used efficiently.
As with all programming concepts, practice makes perfect. Try creating your own nested loop scenarios – maybe a chess board setup, or a weekly school schedule. The possibilities are endless!
Keep coding, keep learning, and most importantly, have fun with it! Until next time, this is your friendly neighborhood computer teacher signing off. Happy looping!
Credits: Image by storyset