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difflib-generated HTML file does not use monospaced font #131204
Description
Bug report
Bug description:
difflib.HtmlDiff.make_file writes an HTML file with a CSS rule specifying Courier as the font to use. On systems which don't have it installed, browsers may fall back to the system default font, which likely won't be monospaced.
import difflib
import webbrowser
hd = difflib.HtmlDiff()
html = hd.make_file(["a", "aab", "c" + "f" * 20, "eg", "ry"], ["aab", "f" * 19, "ry"])
with open("diff.html", "w") as writer:
print(html, file=writer)
webbrowser.open("diff.html")On my system (which does not have Courier), the default font is Signika, which is what Firefox used to render the text.
- Python 3.13.2 (main, Feb 5 2025, 08:05:21) [GCC 14.2.1 20250128]
- glibc 2.41+r9+ga900dbaf70f0-1
- Arch Linux (64-bit)
I think is is sufficient to do:
diff --git a/Lib/difflib.py b/Lib/difflib.py
index bc09aa128aa..11d286a4aa8 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1633,7 +1633,7 @@ def _line_pair_iterator():
_styles = """
:root {color-scheme: light dark}
- table.diff {font-family:Courier; border:medium;}
+ table.diff {font-family:monospace; border:medium;}
.diff_header {background-color:#e0e0e0}
td.diff_header {text-align:right}
.diff_next {background-color:#c0c0c0}and will follow up with a pull request soon.
CPython versions tested on:
3.13
Operating systems tested on:
Linux
Activity
hugovk commentedon Mar 13, 2025
Shall we use the System Font Stack for better cross-platform support?
https://systemfontstack.com/
picnixz commentedon Mar 13, 2025
(I think we can consider it as a bugfix as it hinders readability)
[-]bug: `difflib`-generated HTML file does not use monospaced font[/-][+]`difflib`-generated HTML file does not use monospaced font[/+]gh-131204: Fix `difflib.HtmlDiff` may not use monospaced font (#131221)
[3.12] gh-131204: Fix `difflib.HtmlDiff` may not use monospaced font (G…
[3.13] gh-131204: Fix `difflib.HtmlDiff` may not use monospaced font (G…
[3.12] pythongh-131204: Fix `difflib.HtmlDiff` may not use monospaced…
pythongh-131204: Fix `difflib.HtmlDiff` may not use monospaced font (p…