Looping Through Lists

When working with lists, you will frequently need to loop through every item one by one to inspect, print, or calculate data.

Python makes iterating through lists simple and intuitive.

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1. Looping by Item (for item in list)

The cleanest and most common way to iterate through a list is using a standard for loop:

fruits = ["apple", "banana", "orange", "mango"]

for fruit in fruits:
    print(f"I like {fruit}")

Output:

I like apple
I like banana
I like orange
I like mango

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2. Getting Both Index and Item (enumerate())

If you need both the index position (0, 1, 2...) and the item value at the same time, use Python's built-in enumerate() function:

tasks = ["Write code", "Review PR", "Deploy app"]

for index, task in enumerate(tasks):
    print(f"Task #{index + 1}: {task}")

Output:

Task #1: Write code
Task #2: Review PR
Task #3: Deploy app

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3. Looping by Index (range(len(list)))

If you specifically need to access items by their index numbers:

scores = [85, 92, 78, 90]

for i in range(len(scores)):
    print(f"Student {i}: score is {scores[i]}")

Output:

Student 0: score is 85
Student 1: score is 92
Student 2: score is 78
Student 3: score is 90

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4. Looping with a while Loop

You can also use a while loop with an index counter variable:

colors = ["red", "green", "blue"]
i = 0

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

Output:

red
green
blue

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5. Practical Example: Calculating Total & Average

prices = [120, 250, 80, 450]
total = 0

for price in prices:
    total += price

average = total / len(prices)

print(f"Total Bill: ₹{total}")
print(f"Average Price: ₹{average}")

Output:

Total Bill: ₹900
Average Price: ₹225.0

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Modifying While Iterating

Avoid adding or removing items directly inside a for loop while iterating over the same list, as it alters index positions. If you need to filter elements, create a new filtered list.

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Quick Summary

• Direct Iteration: for item in list: is the most readable, pythonic way to visit every element.
• Indexed Iteration (enumerate): for index, item in enumerate(list): provides both position and value together.
• Length-Based Loop: for i in range(len(list)): allows accessing elements via index subscription list[i].
• While Loop: Uses an explicit index counter (i = 0 up to len(list) - 1).

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What's Next?

Let's understand List Mutability to see how Python allows changing, replacing, and modifying list elements in-place!

List Mutability

Learn why lists are mutable, how in-place modifications work, and compare with strings