PEP 3102 and PEP 570 should say **Keyword-Only Parameters** instead of **Keyword-Only Arguments**

PEP 3102 and PEP 570 say Keyword-Only Arguments but they should say Keyword-Only Parameters because a keyword-only parameter is the parameter which only accepts a keyword argument.

Actually, PEP 570 correctly says Positional-Only Parameters because a positional-only parameter is the parameter which only accepts a positional argument.

Glossary explains a keyword argument and positional argument.

Linked PRs

gh-133438: Fix the use of the terms "argument" and "parameter" in the documentation #135160
gh-133438: Fix the use of the terms "argument" and "parameter" in dis.show_code() #135170
gh-133438: Fix the use of the terms "argument" and "parameter" in error messages for invalid function calls #135172

@AA-Turner

PEPs are historical documents that won't get updates like that and thus they may contain typos or errors. We don't have a policy of publishing erratas though (@AA-Turner maybe it'd be good to have an errata policy?)

Is there anywhere that the error appears in the current documentation? As Ben says, as a
rule we don't tend to update Final PEPs.

A

All occurrences in Cpython:

Modules/_testcapi/getargs.c:/* test PyArg_ParseTupleAndKeywords keyword-only arguments */
Doc/c-api/arg.rst:   keyword-only.  Currently, all keyword-only arguments must also be optional
Doc/whatsnew/3.0.rst:* :pep:`3102`: Keyword-only arguments.  Named parameters occurring
Doc/whatsnew/3.0.rst:  argument list, but you do have keyword-only arguments.
Doc/whatsnew/3.4.rst:keyword-only arguments.  It also provides some efficiency improvements.
Doc/whatsnew/3.4.rst:* Defaults for keyword-only arguments are now evaluated *after* defaults for
Doc/library/unittest.mock.rst:           Added two keyword-only arguments to the reset_mock function.
Doc/library/exceptions.rst:   The optional *name* and *path* keyword-only arguments
Doc/library/functions.rst:   There are two optional keyword-only arguments. The *key* argument specifies
Doc/library/functions.rst:   There are two optional keyword-only arguments. The *key* argument specifies
Doc/library/inspect.rst:      Example: print all keyword-only arguments without default values:
Doc/library/collections.rst:       :ref:`keyword-only arguments <keyword-only_parameter>`.
Doc/library/stdtypes.rst:      (:ref:`keyword-only arguments <keyword-only_parameter>`):
Doc/library/ast.rst:   * ``kw_defaults`` is a list of default values for keyword-only arguments. If
Doc/library/pickle.rst:   class requires keyword-only arguments.  Otherwise, it is recommended for
Doc/library/subprocess.rst:   be set by passing them as keyword-only arguments.
Doc/tutorial/controlflow.rst:Keyword-Only Arguments
Misc/HISTORY:  missing keyword-only arguments. Patch by Jeremiah Lowin.
Misc/HISTORY:- Issue #20619: Give the AST nodes of keyword-only arguments a column and line
Misc/HISTORY:- Issue #14607: Fix keyword-only arguments which started with ``__``.
Misc/HISTORY:- Issue #12356: When required positional or keyword-only arguments are not
Misc/HISTORY:- PEP 3102: keyword-only arguments.
Misc/NEWS.d/3.5.0a3.rst:of instances of classes whose __new__ method takes keyword-only arguments.
Misc/NEWS.d/3.12.0a1.rst:missing keyword-only arguments.
Misc/NEWS.d/3.10.0b1.rst:will become keyword-only arguments to the generated __init__.
Misc/NEWS.d/3.5.0a1.rst:keyword-only arguments. Patch by Jeremiah Lowin.
Lib/_ast_unparse.py:        # varargs, or bare '*' if no varargs but keyword-only arguments present
Lib/_ast_unparse.py:        # keyword-only arguments
Lib/pydoc_data/topics.py:      keyword (keyword-only arguments):
Lib/test/test_positional_only_arg.py:        with self.assertRaisesRegex(TypeError, r"missing 2 required keyword-only arguments: 'd' and 'e'"):
Lib/test/test_positional_only_arg.py:                                               r"\(and 2 keyword-only arguments\) were given"):
Lib/test/test_extcall.py:    TypeError: f() takes 0 positional arguments but 3 positional arguments (and 2 keyword-only arguments) were given
Lib/test/test_extcall.py:    TypeError: f() missing 5 required keyword-only arguments: 'a', 'b', 'c', 'd', and 'e'
Lib/test/test_keywordonlyarg.py:        # more than 255 keyword-only arguments, should compile ok
Lib/inspect.py:    'args' is the list of argument names. Keyword-only arguments are
Lib/inspect.py:    # keyword-only arguments
Lib/inspect.py:        Parameter objects (keyword-only arguments are in the same order
Lib/inspect.py:                # a '*' to separate keyword-only arguments
Lib/copyreg.py:    keyword-only arguments to be pickled correctly.
Python/ast_unparse.c:    /* vararg, or bare '*' if no varargs but keyword-only arguments present */
Python/ast_unparse.c:    /* keyword-only arguments */

There are some that should be fixed.

I think we should generally continue the policy of leaving PEPs as historical docs. In particular, I don't think this issue should be an exception. So either 1) this issue should be closed and a new one opened, with Stan's list copied over; or 2) the title and initial comment should be revised (but then following comments, including this, would not fit). I suggest 1).

For the revised or new issue: in some cases, '-only' should be removed, resulting in 'keyword argument'; in others, s/argument/parameter, as proposed.

the title and initial comment should be revised (but then following comments, including this, would not fit). I suggest 1).

IMO either is fine as for 2), the comments can be marked as "resolved" (or similar) hiding them.

pythongh-133438: Fix the use of the terms "argument" and "parameter" …

There are many other cases of misusing "argument" and "parameter".

#135160 fixes the use of the terms "argument" and "parameter" in the documentation. A following PR will fix also error messages and output.

pythongh-133438: Fix the use of the terms "argument" and "parameter" …

FWIW, I'd keep the phrase keyword-only argument in (most) places where we're really talking about arguments, like “This function accepts a keyword-only foo argument.”
The only is redundant, but it makes it clearer that you can't pass the value positionally.

I'm closing this issue:

PEPs generally are not changed after they are accepted
If we were to change a PEP, we'd do it in https://github.com/python/peps, not this repo
The distinction between arguments and parameters is mostly pedantic, and sometimes depends on your perspective
Litigating every "argument" and "parameter" to decide which is right is a lot of work with little benefit. See gh-133438: Fix the use of the terms "argument" and "parameter" in the documentation #135160 for discussion of this.

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PEP 3102 and PEP 570 should say **Keyword-Only Parameters** instead of **Keyword-Only Arguments** #133438

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picnixz commented on May 5, 2025

AA-Turner commented on May 5, 2025

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PEP 3102 and PEP 570 should say Keyword-Only Parameters instead of Keyword-Only Arguments #133438