List comprehension vs for loop in Python: which is better?
asked 3 months ago364 viewsen
Is [x * 2 for x in nums if x > 0] better than a normal for loop with append? My code reviewer keeps suggesting comprehensions.
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1 Answer
For building a new list from an existing iterable, comprehensions are idiomatic, more concise, and a bit faster (no repeated .append attribute lookup).
positives_doubled = [x * 2 for x in nums if x > 0]Use a regular loop when: - There are side effects (printing, writing to a DB). Don't use a comprehension just to loop. - The logic needs several statements, try/except, or would need nested conditions that hurt readability.
For large data you only iterate once, use a generator expression instead. It doesn't build the whole list in memory:
total = sum(x * 2 for x in nums if x > 0)Sign in to tell others whether this worked.
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