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Always require parentheses for genexps in base class lists #76204

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ncoghlan opened this issue Nov 14, 2017 · 2 comments
Closed

Always require parentheses for genexps in base class lists #76204

ncoghlan opened this issue Nov 14, 2017 · 2 comments
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3.7 interpreter-core type-bug

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@ncoghlan
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@ncoghlan ncoghlan commented Nov 14, 2017

BPO 32023
Nosy @ncoghlan, @serhiy-storchaka
PRs
  • #4400
  • Dependencies
  • bpo-32012: Disallow ambiguous syntax f(x for x in [1],)
  • 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 2017-11-15.15:54:47.629>
    created_at = <Date 2017-11-14.10:25:03.999>
    labels = ['interpreter-core', 'type-bug', '3.7']
    title = 'Always require parentheses for genexps in base class lists'
    updated_at = <Date 2017-11-15.15:54:47.628>
    user = 'https://github.com/ncoghlan'

    bugs.python.org fields:

    activity = <Date 2017-11-15.15:54:47.628>
    actor = 'serhiy.storchaka'
    assignee = 'none'
    closed = True
    closed_date = <Date 2017-11-15.15:54:47.629>
    closer = 'serhiy.storchaka'
    components = ['Interpreter Core']
    creation = <Date 2017-11-14.10:25:03.999>
    creator = 'ncoghlan'
    dependencies = ['32012']
    files = []
    hgrepos = []
    issue_num = 32023
    keywords = ['patch']
    message_count = 2.0
    messages = ['306197', '306275']
    nosy_count = 2.0
    nosy_names = ['ncoghlan', 'serhiy.storchaka']
    pr_nums = ['4400']
    priority = 'low'
    resolution = 'fixed'
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = 'behavior'
    url = 'https://bugs.python.org/issue32023'
    versions = ['Python 3.7']

    @ncoghlan
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    @ncoghlan ncoghlan commented Nov 14, 2017

    The compiler currently allows parentheses to be omitted if a generator expression is the sole entry in a base class list:

        >>> class C(x for x in []): pass
        ... 
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
        TypeError: cannot create 'generator' instances

    The language reference states that the parentheses around a generator expression are only optional for "calls with only one argument": https://docs.python.org/3/reference/expressions.html#generator-expressions

    A base class list is not a call, so this should be treated as a syntax error, rather than being handled as equivalent to class C((x for x in [])): pass

    @ncoghlan ncoghlan added 3.7 interpreter-core type-bug labels Nov 14, 2017
    @serhiy-storchaka
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    @serhiy-storchaka serhiy-storchaka commented Nov 15, 2017

    New changeset ddbce13 by Serhiy Storchaka in branch 'master':
    bpo-32023: Disallow genexprs without parenthesis in class definitions. (bpo-4400)
    ddbce13

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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