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textwrap.shorten() raises "placeholder too large" for text that already fits

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评估

难度
2/5
预计耗时
1-3 小时
新手友好度
45/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
python
领域
backend

调研方向

Start by reading the textwrap implementation of _wrap_chunks() and the tests for textwrap.shorten() and wrap() with max_lines. Reproduce the supplied examples and check where the placeholder width is validated relative to truncation. Done means fitting text is returned without the placeholder error, while existing behavior for text that needs truncation remains covered by tests.

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描述

stdlib type-bug
Bug description

textwrap.shorten() raises ValueError for text that fits in width when
the placeholder is wider than width:

>>> import textwrap
>>> textwrap.shorten('ab', width=4)
Traceback (most recent call last):
  ...
ValueError: placeholder too large for max width

shorten's docstring says such text is returned unchanged: "If it then fits
in the width, it is returned as is." 'ab' fits in width 4.

The same happens in wrap() whenever max_lines is set and the text fits but
the placeholder is wider than width:

>>> textwrap.wrap('hello world', width=20, max_lines=3, subsequent_indent=' ' * 17)
Traceback (most recent call last):
  ...
ValueError: placeholder too large for max width
>>> textwrap.wrap('hello world', width=20, subsequent_indent=' ' * 17)
['hello world']

_wrap_chunks() checks the placeholder-fits guard eagerly, before wrapping,
whenever max_lines is set. But the placeholder is only used when the text is
actually truncated, so the guard fires on text that never needs it.

CPython versions tested on

3.14, 3.15, CPython main branch

Operating systems tested on

macOS

Linked PRs
  • gh-160044
主要语言
Python
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