Windows: python3 command not found in hook scripts

[labagentai]

Bug Description

MemPalace hook scripts (mempal-stop-hook.sh, mempal-precompact-hook.sh) fail on Windows because they use python3 which doesn't exist on Windows. Python is registered as python on Windows.

Error Message

/c/Users/USER/.claude/plugins/cache/mempalace/mempalace/3.0.14/hooks/mempal-stop-hook.sh: line 5: python3: command not found

Affected Files

• hooks/mempal-stop-hook.sh (line 5)
• hooks/mempal-precompact-hook.sh (line 5)

Current Code

echo "$INPUT" | python3 -m mempalace hook run --hook stop --harness claude-code

Suggested Fix

Use a cross-platform Python command resolution. For example:

PYTHON_CMD="${PYTHON_CMD:-$(command -v python3 2>/dev/null || command -v python 2>/dev/null)}"
echo "$INPUT" | "$PYTHON_CMD" -m mempalace hook run --hook stop --harness claude-code

Or simply use python which works on both platforms (Python 3 is now the default python on most systems).

Environment

• OS: Windows 11 Pro
• Shell: Git Bash (bash)
• Python: 3.x (available as python, not python3)
• MemPalace version: 3.0.14
• Harness: Claude Code

[CNCDI]

+1 on macOS (Homebrew Python)

Same root cause bites on macOS too when MemPalace is installed under a non-system Python.

Environment

• macOS 14 (Darwin 25.4.0)
• System python3 → /usr/bin/python3 (Python 3.9.6, no mempalace)
• MemPalace installed via pip3 install mempalace under Homebrew Python 3.11 → /opt/homebrew/bin/python3.11
• MemPalace version: 3.0.14 (from marketplace install)
• Harness: Claude Code

Error

Stop hook error: Failed with non-blocking status code: No module named mempalace

Every session end + every /compact prints this. Non-blocking but visible clutter.

Repro

1. Install MemPalace into a non-system Python (e.g. Homebrew python3.11)
2. Install the plugin via /plugin marketplace add ... && /plugin install mempalace
3. End a session or run /compact — hook tries python3 -m mempalace against system Python and fails

Local workaround (macOS)

sed -i '' 's|python3 -m mempalace|python3.11 -m mempalace|g' \
  ~/.claude/plugins/marketplaces/mempalace/.claude-plugin/hooks/*.sh

Works until next plugin update overwrites the hook files.

Suggested robust fix (endorsing the one in the OP, with small extension for venvs / Homebrew cases)

# Prefer a Python that actually has mempalace installed
if command -v mempalace >/dev/null 2>&1; then
  # mempalace CLI exists — use its shebang's interpreter
  PYTHON_CMD="$(head -1 "$(command -v mempalace)" | sed 's|^#!||')"
elif python3 -c 'import mempalace' 2>/dev/null; then
  PYTHON_CMD=python3
elif python -c 'import mempalace' 2>/dev/null; then
  PYTHON_CMD=python
else
  echo "mempalace module not importable via python3 or python" >&2
  exit 1
fi
echo "$INPUT" | "$PYTHON_CMD" -m mempalace hook run --hook stop --harness claude-code

Advantages:

• Auto-locates the Python that actually has mempalace (Homebrew, venv, pyenv, Windows python, system python3)
• Fails loud with a useful message when module is genuinely missing (vs silent non-blocking error)
• Backwards compatible

Happy to PR if useful.

[yasku]

+1 on macOS (Homebrew Python)

Same root cause bites on macOS too when MemPalace is installed under a non-system Python.

Environment

• macOS 14 (Darwin 25.4.0)
• System python3 → /usr/bin/python3 (Python 3.9.6, no mempalace)
• MemPalace installed via pip3 install mempalace under Homebrew Python 3.11 → /opt/homebrew/bin/python3.11
• MemPalace version: 3.0.14 (from marketplace install)
• Harness: Claude Code

Error

Stop hook error: Failed with non-blocking status code: No module named mempalace

Every session end + every /compact prints this. Non-blocking but visible clutter.

Repro

1. Install MemPalace into a non-system Python (e.g. Homebrew python3.11)
2. Install the plugin via /plugin marketplace add ... && /plugin install mempalace
3. End a session or run /compact — hook tries python3 -m mempalace against system Python and fails

Local workaround (macOS)

sed -i '' 's|python3 -m mempalace|python3.11 -m mempalace|g' \
  ~/.claude/plugins/marketplaces/mempalace/.claude-plugin/hooks/*.sh

Works until next plugin update overwrites the hook files.

Suggested robust fix (endorsing the one in the OP, with small extension for venvs / Homebrew cases)

# Prefer a Python that actually has mempalace installed
if command -v mempalace >/dev/null 2>&1; then
  # mempalace CLI exists — use its shebang's interpreter
  PYTHON_CMD="$(head -1 "$(command -v mempalace)" | sed 's|^#!||')"
elif python3 -c 'import mempalace' 2>/dev/null; then
  PYTHON_CMD=python3
elif python -c 'import mempalace' 2>/dev/null; then
  PYTHON_CMD=python
else
  echo "mempalace module not importable via python3 or python" >&2
  exit 1
fi
echo "$INPUT" | "$PYTHON_CMD" -m mempalace hook run --hook stop --harness claude-code

Advantages:

• Auto-locates the Python that actually has mempalace (Homebrew, venv, pyenv, Windows python, system python3)
• Fails loud with a useful message when module is genuinely missing (vs silent non-blocking error)
• Backwards compatible

Happy to PR if useful.

This is something with i have been struggling a lot just for making it to work, as working with uv and the mismatch version issue from the claude code vs. pypi, the tool fails at as for some reason one execution failed, it lead directly to a new mempalace instance installed, worked around with this. Thanks ⚡️

[skeeper]

+1 — same root cause bites pipx installs on macOS too.

Environment

• macOS 26.4.1 (arm64)
• python3 → Homebrew Python 3.14.3 (/opt/homebrew/bin/python3)
• MemPalace installed via pipx install git+https://github.com/MemPalace/mempalace.git@v3.3.0 → isolated venv at ~/.local/pipx/venvs/mempalace/
• mempalace 3.3.0 (note: PyPI still at 3.2.0, only git/marketplace ship 3.3.0)
• Harness: Claude Code

Errors (every session end + every /compact)

Stop hook error: Failed with non-blocking status code:
/opt/homebrew/opt/python@3.14/bin/python3.14: No module named mempalace
mempalace mcp failed

pipx creates an isolated venv — bare python3 -m mempalace in .mcp.json and hooks/mempal-*-hook.sh can never resolve, because the module lives only inside ~/.local/pipx/venvs/mempalace/.

Good news for @CNCDI's proposed fix: the PYTHON_CMD auto-detect via the mempalace CLI shebang works out of the box for pipx too — pipx's shim at ~/.local/bin/mempalace starts with:

#!/Users/<user>/.local/pipx/venvs/mempalace/bin/python

so head -1 "$(command -v mempalace)" | sed 's|^#!||' returns the venv interpreter. One detection path covers system Python, Homebrew, venv, pyenv, and pipx — no extra logic needed beyond what CNCDI already proposed.

Confirming v3.3.0 (HEAD) still has the bare python3 -m mempalace in both hook scripts and .mcp.json — fix hasn't landed yet. The same replacement needs to happen in .mcp.json command field for the MCP server to resolve.

[fatkobra]

I reproduced the current failure locally in a constrained PATH where only python exists:
both .claude-plugin/hooks/mempal-stop-hook.sh and .claude-plugin/hooks/mempal-precompact-hook.sh fail with python3: command not found.

I have a small fix ready that updates the two plugin hook wrappers to prefer the installed mempalace CLI, then fall back to importable python3 / python, plus execution tests for the wrappers.

I'm intentionally keeping .claude-plugin/.mcp.json / plugin.json out of scope for this PR.

[fatkobra]

Reproduction before the fix:
`❯ SCRIPT=".claude-plugin/hooks/mempal-stop-hook.sh"
TMP="$(mktemp -d)"
mkdir -p "$TMP/bin"

cat > "$TMP/bin/cat" <<'EOF'
#!/bin/sh
exec /bin/cat "$@"
EOF
chmod +x "$TMP/bin/cat"

cat > "$TMP/bin/python" <<EOF
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 0
fi
printf '%s' "$*" > "$TMP/args.txt"
/bin/cat > "$TMP/stdin.json"
printf '{}\n'
EOF
chmod +x "$TMP/bin/python"

PATH="$TMP/bin" /bin/bash "$SCRIPT" <<< '{"session_id":"s1"}'
echo "exit code: $?"
.claude-plugin/hooks/mempal-stop-hook.sh: line 5: python3: command not found
exit code: 127

❯ SCRIPT=".claude-plugin/hooks/mempal-precompact-hook.sh"
TMP="$(mktemp -d)"
mkdir -p "$TMP/bin"

cat > "$TMP/bin/cat" <<'EOF'
#!/bin/sh
exec /bin/cat "$@"
EOF
chmod +x "$TMP/bin/cat"

cat > "$TMP/bin/python" <<EOF
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 0
fi
printf '%s' "$*" > "$TMP/args.txt"
/bin/cat > "$TMP/stdin.json"
printf '{}\n'
EOF
chmod +x "$TMP/bin/python"

PATH="$TMP/bin" /bin/bash "$SCRIPT" <<< '{"session_id":"s1"}'
echo "exit code: $?"
.claude-plugin/hooks/mempal-precompact-hook.sh: line 5: python3: command not found
exit code: 127
`

After the fix:
`❯ SCRIPT=".claude-plugin/hooks/mempal-stop-hook.sh"
TMP="$(mktemp -d)"
mkdir -p "$TMP/bin"

cat > "$TMP/bin/cat" <<'EOF'
#!/bin/sh
exec /bin/cat "$@"
EOF
chmod +x "$TMP/bin/cat"

cat > "$TMP/bin/python" <<EOF
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 0
fi
printf '%s' "$*" > "$TMP/args.txt"
/bin/cat > "$TMP/stdin.json"
printf '{}\n'
EOF
chmod +x "$TMP/bin/python"

PATH="$TMP/bin" /bin/bash "$SCRIPT" <<< '{"session_id":"s1"}'
echo "exit code: $?"
{}
exit code: 0
❯ SCRIPT=".claude-plugin/hooks/mempal-precompact-hook.sh"
TMP="$(mktemp -d)"
mkdir -p "$TMP/bin"

cat > "$TMP/bin/cat" <<'EOF'
#!/bin/sh
exec /bin/cat "$@"
EOF
chmod +x "$TMP/bin/cat"

cat > "$TMP/bin/python" <<EOF
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 0
fi
printf '%s' "$*" > "$TMP/args.txt"
/bin/cat > "$TMP/stdin.json"
printf '{}\n'
EOF
chmod +x "$TMP/bin/python"

PATH="$TMP/bin" /bin/bash "$SCRIPT" <<< '{"session_id":"s1"}'
echo "exit code: $?"
{}
exit code: 0
❯ python -m pytest tests/test_claude_plugin_hook_wrappers.py -v
============================================================================================================ test session starts =============================================================================================================
platform linux -- Python 3.9.25, pytest-8.4.2, pluggy-1.6.0 -- /mnt/ceph-services/base/homes/brreg/extsds/store-my-stuff/gig/mempalace/.venv/bin/python
cachedir: .pytest_cache
rootdir: /mnt/ceph-services/base/homes/brreg/extsds/store-my-stuff/gig/mempalace
configfile: pyproject.toml
plugins: anyio-4.12.1, cov-7.1.0
collected 8 items

tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_prefers_mempalace_cli[mempal-stop-hook.sh-stop] PASSED [ 12%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_prefers_mempalace_cli[mempal-precompact-hook.sh-precompact] PASSED [ 25%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_falls_back_to_importable_python[python3-mempal-stop-hook.sh-stop] PASSED [ 37%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_falls_back_to_importable_python[python3-mempal-precompact-hook.sh-precompact] PASSED [ 50%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_falls_back_to_importable_python[python-mempal-stop-hook.sh-stop] PASSED [ 62%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_falls_back_to_importable_python[python-mempal-precompact-hook.sh-precompact] PASSED [ 75%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_errors_cleanly_when_no_runner_exists[mempal-stop-hook.sh-stop] PASSED [ 87%]
tests/test_claude_plugin_hook_wrappers.py::test_plugin_hook_wrapper_errors_cleanly_when_no_runner_exists[mempal-precompact-hook.sh-precompact] PASSED [100%]

============================================================================================================= 8 passed in 0.23s ==============================================================================================================
❯ SCRIPT=".claude-plugin/hooks/mempal-stop-hook.sh"
TMP="$(mktemp -d)"
mkdir -p "$TMP/bin"

cat > "$TMP/bin/python3" <<'EOF'
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 1
fi
echo "No module named mempalace" >&2
exit 1
EOF
chmod +x "$TMP/bin/python3"

cat > "$TMP/bin/python" <<EOF
#!/bin/sh
if [ "$1" = "-c" ]; then
exit 0
fi
printf '%s' "$*" > "$TMP/args.txt"
/bin/cat > "$TMP/stdin.json"
printf '{}\n'
EOF
chmod +x "$TMP/bin/python"

PATH="$TMP/bin" /bin/bash "$SCRIPT" <<< '{"session_id":"s2"}'
echo "exit code: $?"
cat "$TMP/args.txt"
cat "$TMP/stdin.json"
{}
exit code: 0
-m mempalace hook run --hook stop --harness claude-code{"session_id":"s2"}
`