[MNT]: UserWarning from pyparsing upon immediate import · Issue #24972 · matplotlib/matplotlib · GitHub

Summary

An immediate userwarning on import:

python -W always -c "import matplotlib"

lib/matplotlib/_fontconfig_pattern.py:71: UserWarning: warn_multiple_tokens_in_named_alternation: setting results name 'properties*' on MatchFirst expression will return a list of all parsed tokens in an And alternative, in prior versions only the first token was returned; enclose contained argument in Group

The pyparsing version installed is 3.0.9

Proposed fix

No response

Looks like this just needs what the warning says:

diff --git i/lib/matplotlib/_fontconfig_pattern.py w/lib/matplotlib/_fontconfig_pattern.py
index efc1c9304f..f0ed155c2d 100644
--- i/lib/matplotlib/_fontconfig_pattern.py
+++ w/lib/matplotlib/_fontconfig_pattern.py
@@ -13,7 +13,7 @@ from functools import lru_cache, partial
 import re
 
 from pyparsing import (
-    Optional, ParseException, Regex, StringEnd, Suppress, ZeroOrMore)
+    Group, Optional, ParseException, Regex, StringEnd, Suppress, ZeroOrMore)
 
 from matplotlib import _api
 
@@ -64,7 +64,7 @@ def _make_fontconfig_parser():
     name = Regex(r"[a-z]+")
     value = Regex(r"([^%s]|(\\[%s]))*" % (_value_punc, _value_punc))
     # replace trailing `| name` by oneOf(_CONSTANTS) in mpl 3.9.
-    prop = (name + Suppress("=") + comma_separated(value)) | name
+    prop = Group((name + Suppress("=") + comma_separated(value)) | name)
     return (
         Optional(comma_separated(family)("families"))
         + Optional("-" + comma_separated(size)("sizes"))

[MNT]: UserWarning from pyparsing upon immediate import · Issue #24972 · matplotlib/matplotlib · GitHub

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[MNT]: UserWarning from pyparsing upon immediate import #24972

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[MNT]: UserWarning from pyparsing upon immediate import · Issue #24972 · matplotlib/matplotlib · GitHub

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[MNT]: UserWarning from pyparsing upon immediate import #24972

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Proposed fix

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anntzer commented on Jan 14, 2023

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