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curses.ascii.isblank() function is broken. It confuses backspace (BS 0x08) with tab (0x09) #53979

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kevinpt mannequin opened this issue Sep 4, 2010 · 6 comments
Closed

curses.ascii.isblank() function is broken. It confuses backspace (BS 0x08) with tab (0x09) #53979

kevinpt mannequin opened this issue Sep 4, 2010 · 6 comments
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3.7 (EOL) end of life stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@kevinpt
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kevinpt mannequin commented Sep 4, 2010

BPO 9770
Nosy @4kir4, @serhiy-storchaka
PRs
  • [Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
    		•
    Files
  • curses_ascii_isblank_issue9770.patch: fix isblank, add tests for character classification functions from curses.ascii module
  • curses-ascii-negative.patch
    		•

    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 2016-12-28.08:08:42.885>
created_at = <Date 2010-09-04.00:01:48.509>
labels = ['3.7', 'type-bug', 'library']
title = 'curses.ascii.isblank() function is broken. It confuses backspace (BS 0x08) with tab (0x09)'
updated_at = <Date 2017-03-31.16:36:08.553>
user = 'https://bugs.python.org/kevinpt'

    bugs.python.org fields:

    activity = <Date 2017-03-31.16:36:08.553>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2016-12-28.08:08:42.885>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2010-09-04.00:01:48.509>
creator = 'kevinpt'
dependencies = []
files = ['35693', '45938']
hgrepos = []
issue_num = 9770
keywords = ['patch']
message_count = 6.0
messages = ['115544', '220852', '221008', '223833', '283484', '284161']
nosy_count = 4.0
nosy_names = ['akira', 'kevinpt', 'python-dev', 'serhiy.storchaka']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue9770'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6', 'Python 3.7']
    @kevinpt
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    kevinpt mannequin commented Sep 4, 2010

    The isblank() function defined in curses.ascii is incorrect and doesn't match the output from C's isblank() from ctype.h

    Incorrect definition:
    def isblank(c): return _ctoi(c) in (8,32)

    Should be:
    def isblank(c): return _ctoi(c) in (9,32)

    This most likely affects all versions of Python, not just 2.7.

    @kevinpt kevinpt mannequin added stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Sep 4, 2010
    @BreamoreBoy
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    BreamoreBoy mannequin commented Jun 17, 2014

    The problem and fix are simple but who is best placed to take a look at this?

    @4kir4
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    4kir4 mannequin commented Jun 19, 2014

    I've fixed isblank to accept tab instead of backspace and added tests
    for character classification functions from curses.ascii module that
    have corresponding analogs in ctype.h. They've uncovered issues in
    isblank, iscntrl, and ispunct functions.

    Open questions:

    • is it a security bug (backspace is treated as tab in isblank())?
      If it is then 3.1, 3.2, 3.3 branches should also be updated
      [devguide]. If not then only 2.7, 3.4, and default branches should
      be changed.

      [devguide]: http://hg.python.org/devguide/file/9794412fa62d/devcycle.rst#l105

    • iscntrl() mistakenly returns false for 0x7f but c11 defines it as
      a control character. Should iscntrl behavior (and its docs) be
      changed to confirm? Should another issue be opened?

    • ispunct() mistakenly returns true for control characters such as
      '\n'. The documentation says (paraphrasing) 'any printable except
      space and alnum'. string.printable includes '\n' but 'printing
      character' in C11 does not include the newline. Moreover
      curses.ascii.isprint follows C behavior and excludes control
      characters. Should another issue be opened to return false from
      ispunct() for control characters such as '\n'?

    • ispunct() mistakenly returns true for non-ascii characters such as
      0xff

    • negative integer values: C functions are defined for EOF macros
      (some negative value) and the behavior is undefined for any other
      negative integer value. What should be curses.ascii.is* predicates
      behavior? Should Python guarantee that False is returned?

    • curses.ascii.isspace/.isblank doesn't raise TypeError for bytes,
      None on Python 3

    • should constants from string module be used? What is more
      fundamental: string.digits or curses.ascii.isdigit?

    • no tests for: isascii, isctrl, ismeta (they are not defined in
      ctype.h). It is unclear what the behaviour should be e.g., isascii
      mistakenly returns True for negative ints, ismeta returns True for
      any non-ascii character including Unicode letters. It is not clear
      how isctrl is different from iscntrl.

    @4kir4
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    4kir4 mannequin commented Jul 24, 2014

    I've made the title more explicit: "curses.isblank function doesn't match
    ctype.h" -> "curses.ascii.isblank() function is broken. It confuses
    backspace (BS 0x08) with tab (0x09)"

    If a core developer could review the open questions from the
    previous message msg221008 then I could prepare a proper patch for the
    issue.

    @4kir4 4kir4 mannequin changed the title curses.isblank function doesn't match ctype.h curses.ascii.isblank() function is broken. It confuses backspace (BS 0x08) with tab (0x09) Jul 24, 2014
    @serhiy-storchaka
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    Most issues was fixed in bpo-27079. Except handling negative integers. Following patch fixes the latter issue.

    @serhiy-storchaka serhiy-storchaka added the 3.7 (EOL) end of life label Dec 17, 2016
    @python-dev
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    python-dev mannequin commented Dec 28, 2016

    New changeset cba619a7bf6a by Serhiy Storchaka in branch '3.5':
    Issue bpo-9770: curses.ascii predicates now work correctly with negative integers.
    https://hg.python.org/cpython/rev/cba619a7bf6a

    New changeset 84ca252ac346 by Serhiy Storchaka in branch '2.7':
    Issue bpo-9770: curses.ascii predicates now work correctly with negative integers.
    https://hg.python.org/cpython/rev/84ca252ac346

    New changeset eb81f2d2a42b by Serhiy Storchaka in branch '3.6':
    Issue bpo-9770: curses.ascii predicates now work correctly with negative integers.
    https://hg.python.org/cpython/rev/eb81f2d2a42b

    New changeset 1c0b72996e60 by Serhiy Storchaka in branch 'default':
    Issue bpo-9770: curses.ascii predicates now work correctly with negative integers.
    https://hg.python.org/cpython/rev/1c0b72996e60

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