8000 "SyntaxError: non-default argument follows default argument" confuses · Issue #91210 · python/cpython · GitHub
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Bluenix2 mannequin opened this issue Mar 18, 2022 · 7 comments
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"SyntaxError: non-default argument follows default argument" confuses #91210

Bluenix2 mannequin opened this issue Mar 18, 2022 · 7 comments
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@lysnikolaou
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3.10 only security fixes 3.11 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error

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@Bluenix2
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Bluenix2 mannequin commented Mar 18, 2022
BPO 47054
Nosy @terryjreedy, @gpshead, @vedgar, @pablogsal, @Bluenix2
PRs
  • bpo-47054: Call params parameters not arguments in SyntaxErrors. #32014
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = 'https://github.com/gpshead'
closed_at = None
created_at = <Date 2022-03-18.01:17:42.872>
labels = ['interpreter-core', 'type-bug', '3.10', '3.11']
title = '"SyntaxError: non-default argument follows default argument" confuses'
updated_at = <Date 2022-03-20.21:18:26.112>
user = 'https://github.com/Bluenix2'

    bugs.python.org fields:

    activity = <Date 2022-03-20.21:18:26.112>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2022-03-18.01:17:42.872>
creator = 'bluenix'
dependencies = []
files = []
hgrepos = []
issue_num = 47054
keywords = ['patch']
message_count = 4.0
messages = ['415463', '415469', '415526', '415530']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'gregory.p.smith', 'veky', 'pablogsal', 'bluenix']
pr_nums = ['32014']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47054'
versions = ['Python 3.10', 'Python 3.11']
    @Bluenix2
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    Bluenix2 mannequin commented Mar 18, 2022

    Running the code below will produce a SyntaxError with the message: "non-default argument follows default argument".

        def test(a=None, b):
        return b if a is None else a

    The issue is that a and b aren't arguments, rather, they are parameters. The error message should be changed to: "non-default parameter follows default parameter".

    This change appears simple enough and although it is not something I've found to be troublesome, it will help users to use correct keywords (arguments vs. parameters) when searching on the internet.

    @Bluenix2 Bluenix2 mannequin added 3.7 (EOL) end of life 3.8 (EOL) end of life 3.9 only security fixes 3.10 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) labels Mar 18, 2022
    @vedgar
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    vedgar mannequin commented Mar 18, 2022

    The problem is more subtle. The thing is, "default parameter" doesn't make sense in this context. Yes, a and b are parameter, but a is not "default parameter" in any sensible way. It is _None_ which is the default argument for parameter a, while parameter b has no default argument. In other words, if the function weren't called with a first argument, the default argument would be used.

    So, the fix should be a bit more complicated. Maybe, "a parameter without a default follows a parameter with a default"?

    @Bluenix2
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    Bluenix2 mannequin commented Mar 18, 2022

    Yes I agree, that would be the best.

    @terryjreedy
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    Current message same in 3.11 and 3.9, but I am not sure about backporting to old parser. However merges a change, if any, can decide.

    @terryjreedy terryjreedy added 3.11 only security fixes type-bug An unexpected behavior, bug, or error and removed 3.7 (EOL) end of life 3.8 (EOL) end of life 3.9 only security fixes labels Mar 19, 2022
    @terryjreedy terryjreedy changed the title "SyntaxError: non-default argument follows default argument" should be "parameter" "SyntaxError: non-default argument follows default argument" confuses Mar 19, 2022
    @terryjreedy terryjreedy changed the title "SyntaxError: non-default argument follows default argument" should be "parameter" "SyntaxError: non-default argument follows default argument" confuses Mar 19, 2022
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    @lysnikolaou
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    In addition to this, we fall back to the generic invalid syntax message, in case there are positional-only parameters before the failing ones:

    >>> def test(a=None, b):
  File "<stdin>", line 1
    def test(a=None, b):
                     ^
SyntaxError: non-default argument follows default argument
>>> def test(a, /, b=None, c):
  File "<stdin>", line 1
    def test(a, /, b=None, c):
                            ^
SyntaxError: invalid syntax

    @gpshead you still intend to work on this? I can open a PR for it in case you won't.

    @gpshead
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    gpshead commented Aug 12, 2022

    I've lost track of why I assigned this to myself (I didn't leave myself a comment? tsk tsk), so no, feel free to take it!

    @gpshead gpshead removed their assignment Aug 12, 2022
    @lysnikolaou lysnikolaou self-assigned this Aug 12, 2022
    lysnikolaou added a commit to lysnikolaou/cpython that referenced this issue Aug 12, 2022
    @lysnikolaou
    pythongh-91210: Improve error message when non-default param follows …
    ce567f3 
    …default

- Improve error message when parameter without a default follows one
  with a default
- Show same error message when positional-only params precede the
  default/non-default sequence
    @bedevere-bot bedevere-bot mentioned this issue Aug 12, 2022
    Merged
    miss-islington pushed a commit that referenced this issue Sep 17, 2022
    @lysnikolaou
    gh-91210: Improve error message when non-default param follows default (
    7e36abb 
    GH-95933)

- Improve error message when parameter without a default follows one with a default
- Show same error message when positional-only params precede the default/non-default sequence
    @hauntsaninja
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    Thanks, looks like this has been fixed :-)

    @smheidrich smheidrich mentioned this issue Feb 1, 2025
    Closed
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