With what you look at the output?
Don't you think it's rather a remark to post on stackoverflow, or gitter for pandas ?

It may be normal or not. Before creating an issue on pandas dev, you may have a confirmation per expert user

Better a false alarm than no alarm.

With what you look at the output?
Excel mostly
Don't you think it's rather a remark to post on stackoverflow, or gitter for pandas ?

https://stackoverflow.com/questions/63682677/pandas-to-csv-adds-extra-line-terminator-by-default-winpython-3-8-5-0-pandas

Looks like it's an os thing.

from : https://github.com/pandas-dev/pandas/blob/361166f86da1a665a1b5808e0935c28f8cf56d34/pandas/core/generic.py

line_terminator : str, optional
            The newline character or character sequence to use in the output
            file. Defaults to `os.linesep`, which depends on the OS in which
            this method is called ('\n' for linux, '\r\n' for Windows, i.e.).
            .. versionchanged:: 0.24.0

Somehow the implementation in 3.8.5 now thinks '\r\n' is two lines.

import pandas as pd
import numpy as np
import os
os.linesep = '\n'
df = pd.DataFrame(np.random.randint(0,15,size=(15, 4)), columns=list('ABCD'))
df.to_csv('d://data//df.csv')

gives the correct format in windows

,A,B,C,D
0,12,0,4,9
1,1,6,9,8
2,6,5,14,0
3,12,13,10,4
4,7,4,7,10

Is there an easy way to override os.linesep at system level?

With WinPython3.8.6 the problem persists.