python-poetry/poetry · error · ShellNotSupportedError

Discovered shell '{shell}' doesn't have an activator in virt

Error message

Discovered shell '{shell}' doesn't have an activator in virtual environment

What it means

`ShellNotSupportedError` raised by `poetry env activate` (activate.py:33-39) when `shellingham.detect_shell()` either fails (shell becomes `''`) or returns a shell for which the corresponding activation script does not exist in `env.bin_dir`. The supported scripts are activate.fish/.nu/.csh/.ps1/.bat/activate.

Source

Thrown at src/poetry/console/commands/env/activate.py:37

class ShellNotSupportedError(Exception):
    """Raised when a shell doesn't have an activator in virtual environment"""


class EnvActivateCommand(EnvCommand):
    name = "env activate"
    description = "Print the command to activate a virtual environment."

    def handle(self) -> int:
        try:
            shell, _ = shellingham.detect_shell()
        except shellingham.ShellDetectionFailure:
            shell = ""

        if command := self._get_activate_command(self.env, shell):
            self.line(command)
            return 0

        raise ShellNotSupportedError(
            f"Discovered shell '{shell}' doesn't have an activator in virtual environment"
        )

    def _get_activate_command(self, env: Env, shell: str) -> str:
        if shell == "fish":
            command, filename = "source", "activate.fish"
        elif shell == "nu":
            command, filename = "overlay use", "activate.nu"
        elif shell in ["csh", "tcsh"]:
            command, filename = "source", "activate.csh"
        elif shell in ["powershell", "pwsh"]:
            command, filename = "&", "activate.ps1"
        elif shell == "cmd":
            command, filename = "", "activate.bat"
        elif shell in ["bash", "mksh", "zsh"]:
            command, filename = "source", "activate"
        else:
            command, filename = ".", "activate"

View on GitHub (pinned to 92b74dcfe3)

Solutions

Recreate the venv normally: `poetry env remove python && poetry install`.
Set the shell explicitly via the `SHELL` env var (e.g. `SHELL=/bin/bash poetry env activate`) so shellingham detects it.
Manually source the activator: `<venv>/bin/activate` for bash/zsh.

Example fix

# before
poetry env activate   # ShellNotSupportedError
# after
SHELL=/bin/bash poetry env activate

Defensive patterns

Strategy: fallback

Validate before calling

import os, shutil
shell = os.environ.get("SHELL", "")
if not shell or shutil.which(shell.split("/")[-1]) is None:
    # detection will likely fail; instruct manual activation
    print("set SHELL or source <venv>/bin/activate manually")

Type guard

def has_activator(venv_bin_dir, shell: str) -> bool:
    from pathlib import Path
    mapping = {"fish": "activate.fish", "nu": "activate.nu", "csh": "activate.csh",
               "tcsh": "activate.csh", "powershell": "activate.ps1",
               "pwsh": "activate.ps1", "cmd": "activate.bat",
               "bash": "activate", "mksh": "activate", "zsh": "activate"}
    fname = mapping.get(shell, "activate")
    return (Path(venv_bin_dir) / fname).exists()

Try / catch

from poetry.console.commands.env.activate import ShellNotSupportedError
try:
    ...
except ShellNotSupportedError:
    # fall back to manual activation path
    print(f"source {venv_bin}/activate")

Prevention

Create venvs with full activation scripts (avoid `--without-pip`).
Set `SHELL` explicitly in CI containers.
Keep a manual `source <venv>/bin/activate` documented as fallback.

When it happens

Trigger: Running `poetry env activate` inside a venv that was created without activation scripts (e.g. `--without-pip` or a broken venv); running under a shell shellingham cannot detect (some login managers, containers); the detected shell's script file is missing.

Common situations: CI containers with no real shell; minimal venvs; shells like `xonsh` or `elvish` whose activator was never generated; venv built with `--without-pip` which can skip some scripts.

Related errors

AI-assisted analysis of python-poetry/poetry@92b74dcfe3 (2026-08-04). Data as JSON: /data/errors/62254c32b0b4b5c9.json. Report an issue: GitHub.