Python - csv.writer()

with open("data.csv", "w", newline="", encoding="utf-8") as f Why use newline=""?

Don't we need to break lines?

 

ChatGPT said:

Ah, good question! This is one of those subtle Python csv module quirks. Let me explain carefully.

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1. Why newline=""?

When you open a file for writing CSV in Python:

with open("data.csv", "w", newline="", encoding="utf-8") as f:
    writer = csv.writer(f)
    writer.writerow(["col1", "col2"])

• If you don’t specify newline="", Python’s text mode will translate \n to your platform’s default line ending (\r\n on Windows).

• But the csv module already writes its own \r\n by default.

• Result: On Windows, each row can get extra blank lines between them in the CSV.

Essentially, without newline="", you get double line breaks on Windows.

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2. Does it still break lines?

✅ Yes. Each call to writer.writerow(...) will write a proper line break inside the CSV, even with newline="".

• newline="" prevents Python from adding extra translations.

• The CSV still has normal line breaks (\r\n on Windows, \n on Linux/macOS).

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3. Summary

• Always use newline="" when using Python’s csv module to avoid extra blank lines.

• You don’t lose line breaks; the CSV rows still break correctly.