pypa/pip · error · PipError

Got unexpected number of arguments, expected

Error message

Got unexpected number of arguments, expected {n}. (example: "{prog} config {example}")

What it means

Raised by `pip config` subcommands when the number of positional arguments does not match the expected count. _get_n_args at configuration.py:256 checks `len(args) != n`; each subcommand calls it with its expected n (list=0, get=1, set=2, unset=1, debug=0). The message includes the prog name and an example invocation.

Solutions

  1. Match the argument count: `set` needs key+value (2), `get`/`unset` need key (1), `list`/`debug` need none (0).
  2. Read the example printed in the error message — it shows the exact expected form.
  3. Use `pip config --help` to confirm the subcommand signature.

Example fix

// before
pip config set global.index-url
// after
pip config set global.index-url https://pypi.org/simple
Defensive patterns

Strategy: validation

Validate before calling

# Enforce per-subcommand arity before calling pip config
EXPECTED = {"list": 0, "get": 1, "set": 2, "unset": 1, "debug": 0}

def validate_config_args(subcmd, args):
    if subcmd not in EXPECTED:
        raise ValueError("unknown config subcommand: %s" % subcmd)
    if len(args) != EXPECTED[subcmd]:
        raise ValueError("%s expects %d arg(s), got %d" % (subcmd, EXPECTED[subcmd], len(args)))
    return True

Prevention

When it happens

Trigger: e.g. `pip config set foo` (1 arg, expected 2), `pip config get a b` (2 args, expected 1), or `pip config list extra` (1 arg, expected 0). The mismatch trips configuration.py:258.

Common situations: User forgets the value for set, passes extra tokens to get/list/debug, or misremembers the subcommand arity.

Related errors

AI-assisted analysis of pypa/pip@f399c37189 (2026-08-08). Data as JSON: /api/errors/4153db9dfb4eb41c. Report an issue: GitHub.

Appendix: source

Thrown at src/pip/_internal/commands/configuration.py:263

            )

        try:
            subprocess.check_call(f'{editor} "{fname}"', shell=True)
        except FileNotFoundError as e:
            if not e.filename:
                e.filename = editor
            raise
        except subprocess.CalledProcessError as e:
            raise PipError(f"Editor Subprocess exited with exit code {e.returncode}")

    def _get_n_args(self, args: list[str], example: str, n: int) -> Any:
        """Helper to make sure the command got the right number of arguments"""
        if len(args) != n:
            msg = (
                f"Got unexpected number of arguments, expected {n}. "
                f'(example: "{get_prog()} config {example}")'
            )
            raise PipError(msg)

        if n == 1:
            return args[0]
        else:
            return args

    def _save_configuration(self) -> None:
        # We successfully ran a modifying command. Need to save the
        # configuration.
        try:
            self.configuration.save()
        except Exception:
            logger.exception(
                "Unable to save configuration. Please report this as a bug."
            )
            raise PipError("Internal Error.")

    def _determine_editor(self, options: Values) -> str:

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