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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 (EOL) end of life interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error

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@ncoghlan
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BPO 32023
Nosy @ncoghlan, @serhiy-storchaka
PRs
  • bpo-32023: Disallow genexprs without parenthesis in class definitions. #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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    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 (EOL) end of life interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error labels Nov 14, 2017
    @serhiy-storchaka
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    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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    @ncoghlan @serhiy-storchaka