Unchanged lines detected as changes with difflib.HtmlDiff

Bug report

Bug description:

When running HtmlDiff on test_api_result.response.txt test_api_result.expected.txt (reported at https://github.com/jeffkaufman/icdiff/issues/223) unchanged lines are being detected as changes. Here's the setup:

import difflib
a = open("test_api_result.response.txt").readlines()
b = open("test_api_result.expected.txt").readlines()
with open("tmp.html", "w") as outf:
    outf.write(difflib.HtmlDiff().make_file(a,b))

And the results: https://www.jefftk.com/html-diff-output-repro

I don't see these spurious deltas when running diff:

$ diff test_api_result.*
31,32c31,32
<             'latitude': 1,
<             'longitude': 1,
---
>             'latitude': 1.0,
>             'longitude': 1.0,
40c40
<         'meeting_url': '',
---
>         'meeting_url': None,
77,78c77,78
<             'latitude': 1,
<             'longitude': 1,
---
>             'latitude': 1.0,
>             'longitude': 1.0,
86c86
<         'meeting_url': '',
---
>         'meeting_url': None,
...

CPython versions tested on:

3.13

Operating systems tested on:

macOS

先使用 test_api_result.response.txt 和 test_api_result.expected.txt 重现该报告，然后检查所提供的复现页面上的 HtmlDiff 输出，并将其与 diff 进行比较。当未更改的行不再被标记为更改，同时实际差异仍然可见时，工作就完成了。