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incorrect: failed local variable referenced before assignment #51082

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incorrect: failed local variable referenced before assignment#51082
Labels
type-bugAn unexpected behavior, bug, or error

Description

@paultjuhatwork
paultjuhatwork
mannequin
opened on Sep 3, 2009
BPO 6833
Nosy @mdickinson
Files
  • bug.py: 3 test cases stripped down to the bare minimum
    		•

    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 2009-09-03.11:44:35.275>
created_at = <Date 2009-09-03.11:25:31.158>
labels = ['type-bug', 'invalid']
title = 'incorrect: failed local variable referenced before assignment'
updated_at = <Date 2009-09-03.11:44:35.262>
user = 'https://bugs.python.org/paultjuhatwork'

    bugs.python.org fields:

    activity = <Date 2009-09-03.11:44:35.262>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2009-09-03.11:44:35.275>
closer = 'mark.dickinson'
components = ['None']
creation = <Date 2009-09-03.11:25:31.158>
creator = 'paultjuhatwork'
dependencies = []
files = ['14825']
hgrepos = []
issue_num = 6833
keywords = []
message_count = 2.0
messages = ['92199', '92201']
nosy_count = 2.0
nosy_names = ['mark.dickinson', 'paultjuhatwork']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue6833'
versions = ['Python 2.6', 'Python 2.5', 'Python 2.4', 'Python 3.0']

    Activity

    1. paultjuhatwork commented on Sep 3, 2009

      @paultjuhatwork
      paultjuhatworkmannequin
      on Sep 3, 2009
      MannequinAuthor

      The attached python file will give the following output, which is
      incorrect behavior as far as I know:
      "
      this will fail
      failed local variable 'in_std' referenced before assignment

      this won't fail
      Not failed
      this won't fail either
      Not failed
      "

      This is tested on windows with python2.6(standard msi) and on centos
      5.3 with python2.6 (custom rpm), python2.4 (system rpm), freebsd with
      python2.5 (system package), python2.6 ("hand" compiled) and python3.0
      ("hand" compiled).

      The attached code is stripped down to the bare minimum and therefore
      won't do anything usefull.

    2. paultjuhatwork
      added
      type-bugAn unexpected behavior, bug, or error
      on Sep 3, 2009

    3. mdickinson commented on Sep 3, 2009

      @mdickinson
      mdickinson
      on Sep 3, 2009
      Member

      This is not a bug. The behaviour you're seeing is described here:

      http://docs.python.org/reference/executionmodel.html#naming-and-binding

      "If a name binding operation occurs anywhere within a code block, all
      uses of the name within the block are treated as references to the
      current block. This can lead to errors when a name is used within a
      block before it is bound. This rule is subtle. Python lacks declarations
      and allows name binding operations to occur anywhere within a code
      block. The local variables of a code block can be determined by scanning
      the entire text of the block for name binding operations."

      In the failing example, the registerdecorator function contains an
      assignment to in_std, so by the rules above in_std is local to the
      function. The 'if in_std' line therefore tries to lookup 'in_std' in
      the local namespace; it doesn't exist (yet), so an UnboundLocalError
      exception occurs.

    4. mdickinson
      closed this as completedon Sep 3, 2009
    5. mdickinson
      added
      invalid
      on Sep 3, 2009
    6. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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