email.utils.collapse_rfc2231_value raises AttributeError on non-3-tuples

Bug report

Bug description:

Issue

collapse_rfc2231_value raises AttributeError: 'tuple' object has no attribute 'startswith' when passed a tuple whose length is not 3. The guard if not isinstance(value, tuple) or len(value) != 3 is meant to handle this case, but falls through to unquote(value) which expects a string.

Reproducer

from email.utils import collapse_rfc2231_value
collapse_rfc2231_value(('a', 'b'))
# AttributeError: 'tuple' object has no attribute 'startswith'

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-145825

从 email.utils.collapse_rfc2231_value 开始，使用包含两个元素的元组运行 issue 中的复现程序。确定长度不是三的元组应如何处理，然后添加或更新回归测试覆盖，以便不再发生报告的 AttributeError。关联的 PR gh-145825 表明这项工作已经在进行中。