Why Does My Python CSV File Add Extra Carriage Returns on Windows?

Troubleshooting: CSV File in Python Appends Extra Carriage Return on Windows

While writing a CSV file in Python on a Windows system, an unexpected issue arises where an additional r character appears at the end of each row within the file. This deviation from the expected rn line termination poses a concern, leaving developers wondering about the underlying cause and whether it is an intended behavior.

To delve into the source of this issue, let's analyze the code snippet provided:

import csv

with open('test.csv', 'w') as outfile:
    writer = csv.writer(outfile, delimiter=',', quoting=csv.QUOTE_MINIMAL)
    writer.writerow(['hi', 'dude'])
    writer.writerow(['hi2', 'dude2'])

This code is designed to generate a CSV file named test.csv containing two rows of data: ['hi', 'dude'] and ['hi2', 'dude2']. However, upon inspection of the generated file, we find that each row is suffixed with an additional r character.

To understand this behavior, we turn to the Python documentation for the csv module. According to the documentation, it is recommended to open the file with newline='' on all platforms to disable universal newlines translation.

For Python 3:

By default, on Windows, the csv module uses universal newlines translation, which translates the rn line terminator to n when writing to the file. To prevent this translation and maintain the original rn line terminator, it is necessary to open the file with newline='', as shown below:

with open('output.csv', 'w', newline='', encoding='utf-8') as f:
    writer = csv.writer(f)
    ...

For Python 2:

On Windows for Python 2, it is crucial to open the files in binary mode, using 'rb' or 'wb', before passing them to either csv.reader or csv.writer. Despite the file being a text file, CSV is considered a binary format by the libraries involved, with rn separating records. Writing this separator in text mode prompts the Python runtime to replace n with rn, resulting in the observed rrn sequences in the file. Refer to this previous answer for more details on this aspect.

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