Subprocess - Getting INFO logs in stderr with no error message and returncode is 0

I am using subprocess module to run some bash jobs. Here subprocess is not working expected as it is giving me INFO logs in its stderr object. There is no single log which show any error/exception message. I have tried by running the same bash job using terminal and I am not getting any error there too. Also the return code of the process is 0.

Here is the python code that I am using

backup_name = "base_000000010000000000000005"
time = datetime.utcnow()
file = "/test.sh"
arguments = [file, time.strftime('%Y-%m-%d %H:%M:%S'), backup_name]
proc = subprocess.Popen(arguments, shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = proc.communicate()
print('returncode :{}'.format(proc.returncode))
if stderr:
    print("stderr :")
    print(stderr.decode())

test.sh

wal-g backup-fetch /new_directory $2

On executing the above code,

postgres@test-9:~/restoration$ python3 test.py 
returncode :0
stdout :Params: /vol/restore/postgresql/14/main, base_000000010000000000000005, 2022-11-25 11:20:20

stderr :
INFO: 2022/11/26 09:54:44.264085 Selecting the backup with name base_000000010000000000000005...
INFO: 2022/11/26 09:54:44.425420 Finished decompression of part_003.tar.lz4
INFO: 2022/11/26 09:54:44.425432 Finished extraction of part_003.tar.lz4
INFO: 2022/11/26 09:54:46.261901 Finished extraction of part_001.tar.lz4
INFO: 2022/11/26 09:54:46.261916 Finished decompression of part_001.tar.lz4
INFO: 2022/11/26 09:54:46.286092 Finished decompression of pg_control.tar.lz4
INFO: 2022/11/26 09:54:46.286104 Finished extraction of pg_control.tar.lz4
INFO: 2022/11/26 09:54:46.286108 
Backup extraction complete.

You can see in the above response, there is not a single which is giving any error information all are INFO logs. On executing the same scripts on the shell I got the same response, there is also not any error log.

postgres@test-9:~/restoration$ ./test.sh '2022-11-25 11:30' base_000000010000000000000005
INFO: 2022/11/26 09:54:23.148111 Selecting the backup with name base_000000010000000000000005...
INFO: 2022/11/26 09:54:23.303886 Finished decompression of part_003.tar.lz4
INFO: 2022/11/26 09:54:23.303939 Finished extraction of part_003.tar.lz4
INFO: 2022/11/26 09:54:25.144313 Finished extraction of part_001.tar.lz4
INFO: 2022/11/26 09:54:25.144327 Finished decompression of part_001.tar.lz4
INFO: 2022/11/26 09:54:25.163943 Finished decompression of pg_control.tar.lz4
INFO: 2022/11/26 09:54:25.163960 Finished extraction of pg_control.tar.lz4
INFO: 2022/11/26 09:54:25.163970 
Backup extraction complete.

Version : Python 3.8.10

I have tried by passing every possible argument in Popen, but getting the same response in stderr. Can I get help here, why the INFO logs are coming inside the stderr, as it should be NONE if there is no error.

test.py の Popen 呼び出しと test.sh の wal-g 呼び出しから始め、コマンドを再現して stdout と stderr をシェルから直接実行した場合と比較します。Python 3.8 の subprocess.Popen と communicate のドキュメントを読み、そのうえで wal-g が意図的に INFO ログを stderr に書き込んでいるかを確認します。有用な解決では、発生元と想定されるストリームの挙動を特定します。