T05

Output from python or claude turns into mojibake in a variable

Symptom

Printed straight to the screen it looks fine, but $x = python ... holds garbled characters, and so does the log you write from it.

Check it in 30 seconds

Paste into Windows PowerShell 5.1. It only creates files under your %TEMP% folder. If the last line says REPRODUCED, it happens on your machine.

$d = Join-Path $env:TEMP ('cc-trap-' + (Get-Date -Format 'yyyyMMddHHmmss')); New-Item -ItemType Directory $d -Force | Out-Null
$pyv = & python -c "import sys; print('%d.%d.%d' % sys.version_info[:3])" 2>$null
if (-not $pyv) { 'CANNOT CHECK (python not found, or only the Microsoft Store stub: install Python from python.org)' } else {
"python $pyv"
[IO.File]::WriteAllText("$d\say.py", 'import sys; sys.stdout.buffer.write((chr(0x65e5)+chr(0x672c)).encode("utf-8"))')
$s = python "$d\say.py"
$want = [string][char]0x65E5 + [char]0x672C
"read with code page $([Console]::OutputEncoding.CodePage): " + (($s.ToCharArray() | ForEach-Object { '{0:X4}' -f [int]$_ }) -join ' ') + '  (want 65E5 672C)'
if ($s -ne $want) { 'REPRODUCED' } else { 'NOT REPRODUCED' }
}

Why it happens

PowerShell decodes a native program's output with [Console]::OutputEncoding, which defaults to the OEM code page (437, 850, 932 ...). Output from a program that writes UTF-8 is decoded incorrectly.

Fix

Set [Console]::OutputEncoding to UTF-8 on the reading side, and PYTHONIOENCODING=utf-8 on the Python side (T06). Do both.

[Console]::OutputEncoding = [System.Text.Encoding]::UTF8
$env:PYTHONIOENCODING = 'utf-8'

On the author's machine

two characters became four others

Author's machine: Windows 11 / Windows PowerShell 5.1.26100 / Python 3.13.7 / Claude Code 2.1.304, Japanese Windows (code page 932). Checked 2026-10-20 to 22.

If you searched for

powershell native command output encoding wrong
powershell capture utf-8 output mojibake
[Console]::OutputEncoding utf8

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