readlines() vs iterating the file object

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Accepted Answer

readlines() reads the entire file into memory and returns a Python list where each element is one line including its trailing newline character. So type(lines).__name__ is 'list' and len(lines) is 2. The alternative is to iterate the file object directly: 'for line in f:'. That approach is lazy - it reads one line at a time and uses constant memory no matter how large the file is. For data science work on multi-gigabyte logs or CSVs, iteration beats readlines() every time. Use readlines() only when you genuinely need random access to lines by index.