8000 Some `matplotlib` mathtext yields a `ParseFatalException` · Issue #318 · pyparsing/pyparsing · GitHub
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Some matplotlib mathtext yields a ParseFatalException #318

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heltluke opened this issue Oct 25, 2021 · 7 comments
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Some matplotlib mathtext yields a ParseFatalException #318

heltluke opened this issue Oct 25, 2021 · 7 comments

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@heltluke
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Minimal example

import matplotlib.pyplot as plt

plt.plot(range(5), '.')
plt.title(r"$x \cdot y$")
plt.show()

presently fails with ParseFatalException: Unknown symbol: \cdot, found '\' (at char 2), (line:1, col:3).

Looking at the matplotlib docs, this seems to be somehow related to their use of pyparsing https://github.com/matplotlib/matplotlib/blob/main/lib/matplotlib/_mathtext.py#L15.
@antalszava antalszava mentioned this issue Oct 25, 2021
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@ptmcg
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ptmcg commented Oct 25, 2021 •
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This is a change from 2.4.7.

ParseFatalExceptions were changed to actually be immediately fatal, rather than checking another alternative to see if it might be a match. In the case of this expression, "\cdot" is parsed as a p.single_symbol | p.symbol_name. It fails to match a p.single_symbol, but would match a p.symbol_name. When single_symbol fails, it raises a ParseFatalException, not an ordinary exception - most likely so that the reported error location is closer to the actual error.

This behavior (where ParseFatalException was not immediately reraised) has been this way for a long time, but was raised as an issue this past summer. I think the current behavior is the correct behavior for a ParseFatalException, but perhaps could be modified if mathtext raises a ParseSyntaxException (this would still require code change in pyparsing). I may just push out a 3.0.2 with this particular fix reverted, with a longer-term plan to get this working correctly.

@anntzer
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anntzer commented Oct 26, 2021 •
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Note that this was already fixed (empirically...) in mpl master by https://github.com/matplotlib/matplotlib/pull/21454/files. I'm not really sure I understand your explanation, though, as we fixed that on symbol_name, rather than on single_symbol?

@rrjbca rrjbca mentioned this issue Oct 26, 2021
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@ptmcg
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ptmcg commented Nov 13, 2021

Is this resolved now?

@anntzer
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anntzer commented Nov 14, 2021

We are trying to decide on the right fix on Matplotlib's side, perhaps you can comment on matplotlib/matplotlib#21606?

@rzellem rzellem mentioned this issue Dec 1, 2021
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@ptmcg
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ptmcg commented Jul 11, 2022 •
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Any further requirements on pyparsing here (other than "please stop breaking our stuff by making internal changes in pyparsing")?

@anntzer
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anntzer commented Jul 11, 2022

I think everything is good on Matplotlib's side now.

@ptmcg
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ptmcg commented Jul 11, 2022

Thanks, closing

@ptmcg ptmcg closed this as completed Jul 11, 2022
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@ptmcg @anntzer @heltluke
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