Since feedparser messes with Python’s internals by assigning
to __code__ it needs to import SGMLParseError too. It also
expects SGMLParseError, which was turned into AssertionError by
https://github.com/python/cpython/commit/e34bbfd61f405eef89e8aa50672b0b25022de320

--- feedparser-6.0.10/feedparser/sgml.py.orig	2023-03-18 09:24:50.976316932 +0100
+++ feedparser-6.0.10/feedparser/sgml.py	2023-03-18 09:26:32.971928811 +0100
@@ -28,6 +28,7 @@
 import re
 
 import sgmllib
+from sgmllib import SGMLParseError
 
 __all__ = [
     'sgmllib',
@@ -41,6 +42,7 @@
     'shorttagopen',
     'starttagopen',
     'endbracket',
+    'SGMLParseError',
 ]
 
 # sgmllib defines a number of module-level regular expressions that are
--- feedparser-6.0.10/feedparser/html.py.orig	2023-03-18 09:32:03.647114745 +0100
+++ feedparser-6.0.10/feedparser/html.py	2023-03-18 09:46:05.021142671 +0100
@@ -349,7 +349,7 @@
 
         try:
             return sgmllib.SGMLParser.parse_declaration(self, i)
-        except sgmllib.SGMLParseError:
+        except AssertionError:
             # Escape the doctype declaration and continue parsing.
             self.handle_data('<')
             return i+1
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<div class='path'>path: <a href='/guix/log/?id=22dcd7270fda6921635ca24b855c07c0420aaf13'>root</a>/<a href='/guix/log/tests?id=22dcd7270fda6921635ca24b855c07c0420aaf13'>tests</a>/<a href='/guix/log/tests/offload.scm?id=22dcd7270fda6921635ca24b855c07c0420aaf13'>offload.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/offload.scm?id=22dcd7270fda6921635ca24b855c07c0420aaf13&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-08-25 13:45:27 -0400'>2020-08-25</span></td><td><a href='/guix/commit/tests/offload.scm?id=4b5a6fbc9b754c0ca70d033dd99f17c4f028733a'>offload: Modify the build-machine record to accept multiple systems.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/offload.scm (&lt;build-machine&gt;)[systems]: New field.
[system]: Accessor changed to %build-machine-system.  Default to #f.
* guix/scripts/offload.scm (build-machine-system): Wrap %build-machine-system
with a deprecation warning.
(build-machine-systems): Access the new systems field or fallback to use
build-machine-system, for backward compatibility.
(machine-matches?): Adjust.
* tests/offload.scm: Add tests...
* Makefile.am (SCM_TESTS): ...and register them.
* doc/guix.texi (Daemon Offload Setup): Update doc.
</span></span></td><td>Maxim Cournoyer</td></tr>