MusicXML export fails on "check_simultan self.sections.pop()" #76

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1. uliska commented on Oct 23, 2016

   

   uliska

   on Oct 23, 2016

   Last edited by uliska

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   Note that this file can only be compiled in the original context as otherwise the includes cannot be resolved.

   I suspected this failed include could be the reason but when placing the flattened file in the original context a) it became compilable and b) the MusicXML export fails with the same message. So this is not the issue.

   The other thing is that I tried that with python-ly from Git (where the OP obviously has the packaged version), and the error is the same. So that isn't a reason either.
2. uliska

   added

   bug

   on Oct 23, 2016
3. PeterBjuhr

   added

   musicxml export

   on Nov 19, 2016
4. mtarenskeen commented on Nov 6, 2019

   

   mtarenskeen

   on Nov 6, 2019

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   I bumped into this bug when trying a very simple test:

   1. create a very simple minimal.ly test with for example only { c' d' e' f' }
   2. ly musicxml minimal.ly -o minimal.musicxml
   3. musicxml2ly minimal.musicxml -o minimal2.ly
   4. ly musicxml minimal2.ly -o minimal2.musicxml

   Unknown command: \mergeDifferentlyDottedOn
   Unknown command: \mergeDifferentlyHeadedOn
   Warning: End not implemented!
   'NoneType' object has no attribute 'merge_voice'
   Traceback (most recent call last):
   File "/usr/bin/ly", line 4, in
   sys.exit(main())
   File "/usr/lib/python3.7/site-packages/ly/cli/main.py", line 288, in main
   c.run(options, cursor, output)
   File "/usr/lib/python3.7/site-packages/ly/cli/command.py", line 221, in run
   writer.parse_document(cursor.document, absolute)
   File "/usr/lib/python3.7/site-packages/ly/musicxml/lymus2musxml.py", line 119, in parse_document
   self.parse_tree(mustree)
   File "/usr/lib/python3.7/site-packages/ly/musicxml/lymus2musxml.py", line 133, in parse_tree
   self.parse_nodes(mus_nodes)
   File "/usr/lib/python3.7/site-packages/ly/musicxml/lymus2musxml.py", line 145, in parse_nodes
   func_call(m)
   File "/usr/lib/python3.7/site-packages/ly/musicxml/lymus2musxml.py", line 624, in End
   self.mediator.check_simultan()
   File "/usr/lib/python3.7/site-packages/ly/musicxml/ly2xml_mediator.py", line 293, in check_simultan
   self.sections.pop()
   IndexError: pop from empty list
5. mtarenskeen commented on Nov 6, 2019

   

   mtarenskeen

   on Nov 6, 2019

   Last edited by mtarenskeen

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   As a workaround I changed line 293 in ly2xml_mediator.py. I am not enough of a Python programmer to judge if this makes any sense, but it worked for me now.

           # self.sections.pop()
           if self.sections:
               self.sections.pop()
   
   
6. shoorick commented on Apr 23, 2022

   

   shoorick

   on Apr 23, 2022

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   The same situation in 2022. As written in previous comment it's possible to patch /usr/lib/python3/dist-packages/ly/musicxml/ly2xml_mediator.py — different lines but the same code

   301c301,302
   <         self.sections.pop()
   ---
   >         if self.sections:
   >             self.sections.pop()
7. fedelibre commented on Feb 6, 2026

   

   fedelibre

   on Feb 6, 2026

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   It's probably a workaround to avoid the error, but not the best solution to fix the underlying bug. I'm not able to help.
8. bmjcode commented on Feb 7, 2026

   

   bmjcode

   on Feb 7, 2026

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   @fedelibre Testing that self.sections isn't empty before pop()-ing it is basic defensive programming. It should be in there regardless of whether there's another underlying bug. I just merged #184 which should hopefully fix this.
9. fedelibre commented on Apr 1, 2026

   

   fedelibre

   on Apr 1, 2026

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   Fixed by #184
10. fedelibre

    closed this as completedon Apr 1, 2026