Confusing error message when constructing invalid inspect.Parameters

[anntzer]

BPO	33197
Nosy	@serhiy-storchaka, @1st1, @corona10, @nitishch
PRs	bpo-33197: Update error message of invalid inspect.Parameters #6636 [3.7] bpo-33197: Update a error message of invalid inspect.Parameters. (GH-6636) #7204 [3.6] bpo-33197: Update a error message of invalid inspect.Parameters. (GH-6636) #7205 bpo-33197: Add description property for _ParameterKind #7206 bpo-33197: Add versionadded tag to the documentation of ParameterKind #7536

^{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 = None
closed_at = <Date 2018-06-08.16:08:08.034>
created_at = <Date 2018-04-01.07:14:32.079>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'Confusing error message when constructing invalid inspect.Parameters'
updated_at = <Date 2018-06-08.16:08:08.033>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2018-06-08.16:08:08.033>
actor = 'yselivanov'
assignee = 'none'
closed = True
closed_date = <Date 2018-06-08.16:08:08.034>
closer = 'yselivanov'
components = ['Library (Lib)']
creation = <Date 2018-04-01.07:14:32.079>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 33197
keywords = ['patch']
message_count = 17.0
messages = ['314764', '314798', '314799', '315900', '317289', '317995', '318041', '318046', '318052', '319006', '319014', '319015', '319060', '319069', '319081', '319083', '319084']
nosy_count = 4.0
nosy_names = ['serhiy.storchaka', 'yselivanov', 'corona10', 'nitishch']
pr_nums = ['6636', '7204', '7205', '7206', '7536']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33197'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[anntzer]

Python 3.6.4

In [15]: inspect.Parameter("foo", kind=inspect.Parameter.VAR_KEYWORD, default=42)
\---------------------------------------------------------------------------

    ValueError                                Traceback (most recent call last)
    <ipython-input-15-7ed8c4fd15f3> in <module>()
    ----> 1 inspect.Parameter("foo", kind=inspect.Parameter.VAR_KEYWORD, default=42)

/usr/lib/python3.6/inspect.py in __init__(self, name, kind, default, annotation)
2442             if kind in (_VAR_POSITIONAL, _VAR_KEYWORD):
2443                 msg = '{} parameters cannot have default values'.format(kind)
-> 2444                 raise ValueError(msg)
2445         self._default = default
2446         self._annotation = annotation

ValueError: 4 parameters cannot have default values

Note the "interesting" error message that starts with "4 parameters ..." (yes, I guess that inspect.Parameter == 4 internally...).

Probably just a matter of making the error f'{kind.name} parameters ...'.

[nitishch]

@antony Lee since you know the fix, do you want to submit a PR?

[nitishch]

Also, _ParameterKind class has a __str__ method. So, I guess it's better to use "{!s}" in the format string instead of using kind.name.

[corona10]

@nitish

I will take a look this issue.
I agree with to use "{!s}" in the format string

[corona10]

Can I get a code review for PR 6636?

[corona10]

PR 6636 is ready to be merged :)

[1st1]

New changeset a9cab43 by Yury Selivanov (Dong-hee Na) in branch 'master':
bpo-33197: Update a error message of invalid inspect.Parameters. (GH-6636)
a9cab43

[1st1]

New changeset cb055bc by Yury Selivanov (Miss Islington (bot)) in branch '3.7':
bpo-33197: Update a error message of invalid inspect.Parameters. (GH-6636) (GH-7204)
cb055bc

[1st1]

New changeset 5e9e9db by Yury Selivanov (Miss Islington (bot)) in branch '3.6':
bpo-33197: Update a error message of invalid inspect.Parameters. (GH-6636) (bpo-7205)
5e9e9db

[corona10]

@yselivanov

Please take a look PR 7206 :)

[1st1]

New changeset 4aa3006 by Yury Selivanov (Dong-hee Na) in branch 'master':
bpo-33197: Add description property for _ParameterKind. (GH-7206)
4aa3006