[Bug]: Pyparsing warnings emitted in mathtext

Bug summary

When plotting anything with at least one logarithmic axes (plt.semilogx(), plt.semilogy(), plt.loglog()) I get two warnings emitted due to code in _mathtext.py. These warnings are not emitted by default, but appears when running Python with e.g. -Wdefault.

Code for reproduction

import matplotlib.pyplot as plt
plt.semilogx([1, 2], [3, 4])
plt.savefig('plot.png')

Actual outcome

/path/to/python/lib/python3.9/site-packages/matplotlib/_mathtext.py:1871: UserWarning: warn_name_set_on_empty_Forward: setting results name 'sym' on Forward expression that has no contained expression
  - p.placeable("sym"))
/path/to/python/lib/python3.9/site-packages/matplotlib/_mathtext.py:1876: UserWarning: warn_ungrouped_named_tokens_in_collection: setting results name 'name' on ZeroOrMore expression collides with 'name' on contained expression
  "{" + ZeroOrMore(p.simple | p.unknown_symbol)("name") + "}")

Expected outcome

No warnings/text should be printed.

Additional information

To see the warnings from the above code, save it to e.g. test.py and run it as either

python -Wdefault test.py

or

PYTHONWARNINGS=default python test.py

The two warnings are triggered by the following lines within matplotlib/_mathtext.py:

        p.accent <<= (
            csnames("accent", [*self._accent_map, *self._wide_accents])
            - p.placeable("sym")

        p.operatorname <<= cmd(
            r"\operatorname",
            "{" + ZeroOrMore(p.simple | p.unknown_symbol)("name") + "}")

where the various attributes on p are instances of pyparsing.Forward.

The warnings appear with Pyparsing versions 3.0.0–3.0.9 but not prior to 3.0.0 (e.g. 2.4.7). Also, the warnings only appear for Matplotlib versions 3.6.0–3.6.3, not e.g. 3.5.3

Operating system

Linux Mint 20

Matplotlib Version

3.6.3

Matplotlib Backend

QtAgg

Python version

3.8.5

Installation

pip

@jmd-dk

Thanks for the clear report @jmd-dk. After a couple of false starts (!) I have reproduced this with main:

/home/ruth/git_stuff/matplotlib/lib/matplotlib/_mathtext.py:1880: UserWarning: warn_name_set_on_empty_Forward: setting results name 'sym' on Forward expression that has no contained expression
  - p.placeable("sym"))
/home/ruth/git_stuff/matplotlib/lib/matplotlib/_mathtext.py:1885: UserWarning: warn_ungrouped_named_tokens_in_collection: setting results name 'name' on ZeroOrMore expression collides with 'name' on contained expression
  "{" + ZeroOrMore(p.simple | p.unknown_symbol)("name") + "}")

The second warning is fixed by #25200 (which was coincidentally opened just before this bug report :)).

The other warning can be suppressed with

diff --git i/lib/matplotlib/_mathtext.py w/lib/matplotlib/_mathtext.py
index b41dca9d69..71af0dfdea 100644
--- i/lib/matplotlib/_mathtext.py
+++ w/lib/matplotlib/_mathtext.py
@@ -13,6 +13,7 @@ import types
 import unicodedata

 import numpy as np
+import pyparsing
 from pyparsing import (
     Empty, Forward, Literal, NotAny, oneOf, OneOrMore, Optional,
     ParseBaseException, ParseException, ParseExpression, ParseFatalException,
@@ -1875,9 +1876,11 @@ class Parser:

         p.customspace <<= cmd(r"\hspace", "{" + p.float_literal("space") + "}")

-        p.accent <<= (
-            csnames("accent", [*self._accent_map, *self._wide_accents])
-            - p.placeable("sym"))
+        with cbook._setattr_cm(
+                pyparsing.__diag__, warn_name_set_on_empty_Forward=False):
+            p.accent <<= (
+                csnames("accent", [*self._accent_map, *self._wide_accents])
+                - p.placeable("sym"))

         p.function <<= csnames("name", self._function_names)
         p.operatorname <<= cmd(

but it's not really clear to me whether it's actually warning about a problematic practice or not (one could move the definition of placeable above the one of accent to suppress the warning, but that actually changes the parsing behavior.

Filter matplotlib-related warnings

Filter matplotlib-related warnings (#2344)

just came across the very same problem which made our CI pipeline "red" (as run with python -We) after a matplotlib update - would be great address this issue!
Thanks

Work around pyparsing diagnostic warnings

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[Bug]: Pyparsing warnings emitted in mathtext #25204

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[Bug]: Pyparsing warnings emitted in mathtext #25204

Description

Bug summary

Code for reproduction

Actual outcome

Expected outcome

Additional information

Operating system

Matplotlib Version

Matplotlib Backend

Python version

Installation

Activity

rcomer commented on Feb 12, 2023

anntzer commented on Feb 12, 2023

anntzer commented on Feb 12, 2023

slayoo commented on Jan 22, 2024

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