pypa/pip · error · CommandError

<dynamic: PEP723 exception message (exc.msg)>

Error message

<dynamic: PEP723 exception message (exc.msg)>

What it means

Raised by RequirementCommand.get_requirements() in req_command.py:406 when pep723_metadata() raises a PEP723Exception while parsing the inline metadata block from a script passed to --requirements-from-script. The PEP723Exception is caught and re-raised as a CommandError with exc.msg. Possible causes include: no PEP 723 block found, multiple blocks found, or invalid TOML inside the block.

Source

Thrown at src/pip/_internal/cli/req_command.py:406

                    isolated=options.isolated_mode,
                    user_supplied=True,
                    config_settings=(
                        parsed_req.options.get("config_settings")
                        if parsed_req.options
                        else None
                    ),
                )
                requirements.append(req_to_add)

        if options.requirements_from_scripts:
            if len(options.requirements_from_scripts) > 1:
                raise CommandError("--requirements-from-script can only be given once")

            script = options.requirements_from_scripts[0]
            try:
                script_metadata = pep723_metadata(script)
            except PEP723Exception as exc:
                raise CommandError(exc.msg)

            script_requires_python = script_metadata.get("requires-python", "")

            if script_requires_python and not options.ignore_requires_python:
                target_python = make_target_python(options)

                if not check_requires_python(
                    requires_python=script_requires_python,
                    version_info=target_python.py_version_info,
                ):
                    raise UnsupportedPythonVersion(
                        f"Script {script!r} requires a different Python: "
                        f"{target_python.py_version} not in {script_requires_python!r}"
                    )

            for req in script_metadata.get("dependencies", []):
                req_to_add = install_req_from_req_string(
                    req,

View on GitHub (pinned to d7d0d0a394)

Solutions

1. Ensure the script contains exactly one `# /// script` block with valid TOML.
2. Validate the TOML content separately: `python -c "import tomllib; tomllib.loads(open('block.txt').read())"`.
3. Check for common TOML errors: unquoted strings, trailing commas, invalid key names.
4. If the script has no dependencies, add an empty block: `# /// script\n# ///`.

Example fix

# before (missing or malformed PEP 723 block)
# myscript.py has no metadata block
pip install --requirements-from-script myscript.py

# after
# myscript.py contains:
# /// script
# dependencies = ["requests", "rich"]
# ///
pip install --requirements-from-script myscript.py

import re
from pip._internal.utils.compat import tomllib

def validate_pep723_script(filepath):
    """Validate a script has exactly one parseable PEP 723 block."""
    regex = r"(?m)^# /// (?P<type>[a-zA-Z0-9-]+)$\s(?P<content>(^#(| .*)$\s)+)^# ///$"
    with open(filepath, encoding='utf8') as f:
        script = f.read()
    matches = [m for m in re.finditer(regex, script) if m.group('type') == 'script']
    if len(matches) == 0:
        return False, 'No PEP 723 script block found'
    if len(matches) > 1:
        return False, 'Multiple PEP 723 script blocks found'
    content = ''.join(l[2:] if l.startswith('# ') else l[1:]
                      for l in matches[0].group('content').splitlines(keepends=True))
    try:
        tomllib.loads(content)
    except Exception as e:
        return False, f'Invalid TOML: {e}'
    return True, None

from pip._internal.exceptions import CommandError
try:
    # pip install --requirements-from-script script.py
except CommandError as e:
    # check if it's a PEP723 parse error
    if 'metadata' in str(e).lower() or 'TOML' in str(e).lower():
        # fix the script's PEP 723 block

When it happens

Trigger: Calling `pip install --requirements-from-script myscript.py` where myscript.py either: (a) has no `# /// script` PEP 723 metadata block, (b) has multiple such blocks, or (c) has a block with malformed TOML content (e.g., invalid syntax, unparseable keys).

Common situations: Forgetting to add the PEP 723 metadata block to a script. Malformed TOML in the dependencies list (e.g., missing quotes, invalid syntax). Copy-pasting a partial PEP 723 block. Using a script that was intended for a different inline metadata type.

Related errors

• --requirements-from-script can only be given once
• Script {script!r} requires a different Python: {target_pytho
• Multiple {name!r} blocks found in {scriptfile!r}
• Failed to parse TOML in {scriptfile!r}
• File does not contain {name!r} metadata: {scriptfile!r}

AI-assisted analysis of pypa/pip@d7d0d0a394 (2026-08-04). Data as JSON: /data/errors/8de4c4c12c472696.json. Report an issue: GitHub.