For Loop vs List Comprehension: Which is Better?

Both for loops and list comprehensions are used to iterate over sequences, but they have key differences in performance, readability, and use cases.

1. Key Differences

Feature	For Loop	List Comprehension
Performance	Slower (due to explicit looping)	Faster (optimized in C)
Readability	More readable for complex logic	Concise for simple operations
Memory Usage	Can be more efficient with generators	Creates a new list in memory
Best For	Complex logic, multiple operations	Simple transformations and filtering

2. Example Comparisons

Basic Example: Squaring Numbers

Using For Loop

numbers = [1, 2, 3, 4, 5]
squared = []

for num in numbers:
    squared.append(num ** 2)

print(squared)

🔹 Output: [1, 4, 9, 16, 25]

Using List Comprehension

numbers = [1, 2, 3, 4, 5]
squared = [num ** 2 for num in numbers]

print(squared)

✅ More concise and faster!

3. Performance Comparison

For large datasets, list comprehensions are much faster because they run at C-speed internally.

Speed Test

import time

numbers = list(range(1000000))

# For Loop
start = time.time()
squared_loop = []
for num in numbers:
    squared_loop.append(num ** 2)
end = time.time()
print("For Loop Time:", end - start)

# List Comprehension
start = time.time()
squared_list_comp = [num ** 2 for num in numbers]
end = time.time()
print("List Comprehension Time:", end - start)

✅ **List comprehension is around 30-40% faster than a for loop!

4. When to Use For Loop vs List Comprehension

✔️ Use For Loop When:

You have complex logic (multiple conditions, nested loops).
You need to modify elements conditionally.
You want better readability for long operations.

✔️ Use List Comprehension When:

You need a quick transformation of a list.
The operation is simple and easy to read.
You need better performance for large data.

5. Which is Better?

👉 For simple operations → List Comprehension (faster, cleaner)
👉 For complex logic → For Loop (easier to read, debug)

🚀 Best Practice: Use list comprehension for simple tasks and for loops for complex ones!

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