Redirecting python output to a file causes UnicodeEncodeError on Windows

Question

I'm trying to redirect output of python script to a file. When output contains non-ascii characters it works on macOS and Linux, but not on Windows.

I've deduced the problem to a simple test. The following is what is shown in Windows command prompt window. The test is only one print call.

Microsoft Windows [Version 10.0.17134.472]
(c) 2018 Microsoft Corporation. All rights reserved.

D:\>set PY
PYTHONIOENCODING=utf-8

D:\>type pipetest.py
print('\u0422\u0435\u0441\u0442')

D:\>python pipetest.py
Тест

D:\>python pipetest.py > test.txt

D:\>type test.txt
Тест

D:\>type test.txt | iconv -f utf-8 -t utf-8
Тест

D:\>set PYTHONIOENCODING=

D:\>python pipetest.py
Тест

D:\>python pipetest.py > test.txt
Traceback (most recent call last):
  File "pipetest.py", line 1, in <module>
    print('\u0422\u0435\u0441\u0442')
  File "C:\Python\Python37\lib\encodings\cp1252.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-3: character maps to <undefined>

D:\>python -V
Python 3.7.2

As one can see setting PYTHONIOENCODING environment variable helps but I don't understand why it needed to be set. When output is terminal it works but if output is a file it fails. Why does cp1252 is used when stdout is not a console?

Maybe it is a bug and can be fixed in Windows version of python?

Answer 1

Based on Python documentation, Windows version use different character encoding on console device (utr-8) and non-character devices such as disk files and pipes (system locale). PYTHONIOENCODING can be used to override it.

https://docs.python.org/3/library/sys.html#sys.stdout

Another method is change the encoding directly in the program, I tried and it works fine.

sys.stdout.reconfigure(encoding='utf-8')

https://docs.python.org/3/library/io.html#io.TextIOWrapper.reconfigure