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MusicXML `<segno/>` in a `<barline>` isn't read, so expandRepeats() fails

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难度
3/5
预计耗时
半天
新手友好度
62/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
python, xml
领域
data

调研方向

The MusicXML importer lives in music21/musicxml, where barline children are parsed; the segno is read for directions but not for <barline>. Start by reproducing with the snippet in the issue and checking what expandRepeats() sees in music21/repeat.py. Done when a segno inside <barline> is attached to the measure so the D.S. expansion gives C, D, E, D, E, with a regression test added beside the existing repeat tests.

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描述

music21 version

10.5.0

Problem summary

MusicXML allows a <segno> (and a <coda>) inside a <barline>, as well as in a direction. The importer doesn't read it from a barline, so a later D.S. has no segno to go to, and expandRepeats() raises.

Steps to reproduce

from music21 import converter

def measure(number, step, before="", after=""):
    return (f'<measure number="{number}">{before}<note><pitch><step>{step}</step>'
            f'<octave>4</octave></pitch><duration>4</duration><type>whole</type></note>{after}</measure>')

xml = f'''<score-partwise version="4.0">
  <part-list><score-part id="P1"><part-name>Music</part-name></score-part></part-list>
  <part id="P1">
    {measure(1, "C", "<attributes><divisions>1</divisions></attributes>")}
    {measure(2, "D", '<barline location="left"><segno/></barline>')}
    {measure(3, "E", after="<direction><direction-type><words>D.S.</words></direction-type></direction>")}
  </part>
</score-partwise>'''

converter.parse(xml, format='musicxml').expandRepeats()

Expected vs. actual behavior

Expected the notes ['C', 'D', 'E', 'D', 'E']. Actual:

music21.repeat.ExpanderException: cannot expand Stream: badly formed repeats or repeat expressions

Writing the same segno as <direction><direction-type><segno/></direction-type></direction> gives the expected result, so only the barline placement is affected.

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