🔁 Python Loop Lists – for, while, enumerate, and Comprehensions

🧲 Introduction – Why Loop Through Lists?

Looping through lists is a fundamental part of Python programming. Whether you’re printing items, filtering data, or applying transformations, looping over lists helps you work with collections efficiently.

Python provides several ways to loop through lists using for, while, and built-in functions like enumerate() and range().

🎯 In this guide, you’ll learn:

• How to loop through lists using for and while loops
• How to access both index and value with enumerate()
• How to loop through lists using range() and list comprehensions
• Best practices and real-world applications

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🔁 Looping with for Loop

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

✅ Explanation:

• Iterates over each element in the fruits list.
• fruit takes the value of each item, one by one.
• print(fruit) outputs: apple banana cherry

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🔢 Looping with Index Using range(len())

for i in range(len(fruits)):
    print(i, fruits[i])

✅ Explanation:

• range(len(fruits)) generates a range of indices: 0, 1, 2.
• fruits[i] accesses the item at each index.
• Output: 0 apple 1 banana 2 cherry

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🔁 Looping with while Loop

i = 0
while i < len(fruits):
    print(fruits[i])
    i += 1

✅ Explanation:

• Initializes i to 0.
• Loops while i is less than the length of the list.
• Prints each item, then increments i by 1.

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🧮 Looping with enumerate()

for index, value in enumerate(fruits):
    print(index, value)

✅ Explanation:

• enumerate(fruits) returns both index and item.
• index is the position, value is the element.
• Output: 0 apple 1 banana 2 cherry

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🎯 List Comprehension for Looping

upper_fruits = [fruit.upper() for fruit in fruits]
print(upper_fruits)

✅ Explanation:

• Converts each fruit name to uppercase.
• Stores results in a new list: ['APPLE', 'BANANA', 'CHERRY'].

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🧪 Loop with break and continue

✅ break Example:

for fruit in fruits:
    if fruit == "banana":
        break
    print(fruit)

Explanation:

• Stops the loop when "banana" is found.
• Only "apple" is printed.

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✅ continue Example:

for fruit in fruits:
    if fruit == "banana":
        continue
    print(fruit)

Explanation:

• Skips "banana" but continues the loop.
• Prints: apple cherry

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💡 Best Practices

• ✅ Use for for clean and direct iteration.
• ✅ Use enumerate() when you need both index and value.
• ✅ Avoid modifying a list while looping over it—use a copy or list comprehension.
• ✅ Use list comprehensions for transformations and filtering.

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📌 Summary – Recap & Next Steps

Looping through lists allows you to process, display, and manipulate each item effectively. Python offers versatile tools from simple for loops to expressive list comprehensions.

🔍 Key Takeaways:

• ✅ Use for loops for readable, direct iteration.
• ✅ Use range(len()) or enumerate() for indexed access.
• ✅ while loops are useful for custom iteration logic.
• ✅ List comprehensions offer concise, readable list transformations.

⚙️ Real-World Relevance:
Used in data processing, automation scripts, file parsing, and API response handling, list loops are essential in nearly every Python project.

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❓ FAQ Section – Python Loop Lists

❓ How do I loop through a list in Python?

✅ Use a for loop:

for item in my_list:
    print(item)

❓ How do I get both index and value in a list loop?

✅ Use enumerate():

for index, value in enumerate(my_list):
    print(index, value)

❓ Can I use while to loop through a list?

✅ Yes, by using an index:

i = 0
while i < len(my_list):
    print(my_list[i])
    i += 1

❓ What’s the difference between break and continue?

✅ break exits the loop immediately; continue skips the current iteration and moves to the next.

❓ How can I convert a list to uppercase using loops?

✅ Use a list comprehension:

new_list = [item.upper() for item in my_list]

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