Skip to content

Fix MEI importer silently dropping <bTrem> and shifting subsequent onsets (AI) #2000

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
mscuthbert merged 1 commit into from
Aug 20, 2026
Merged

Fix MEI importer silently dropping <bTrem> and shifting subsequent onsets (AI) #2000

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
112 changes: 106 additions & 6 deletions music21/mei/base.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,7 @@
from music21 import duration
from music21 import environment
from music21 import exceptions21
from music21 import expressions
from music21 import instrument
from music21 import interval
from music21 import key
Expand Down Expand Up @@ -272,6 +273,21 @@ class MeiElementError(exceptions21.Music21Exception):
_BAD_VERSE_NUMBER = 'Verse number must be an int (got "{}")'


# Mapping from an MEI <bTrem> @unitdur (the note value of one tremolo repetition) to the number of
# tremolo marks used by :class:`~music21.expressions.Tremolo`: an eighth-note unit is one mark, a
# sixteenth two, and so on (log2(unitdur) - 2). Durations outside this table produce no marks.
_MEI_UNITDUR_TO_TREMOLO_MARKS = {
'8': 1,
'16': 2,
'32': 3,
'64': 4,
'128': 5,
'256': 6,
'512': 7,
'1024': 8,
}


# Module-level Functions
# -----------------------------------------------------------------------------
class MeiToM21Converter:
Expand Down Expand Up @@ -2632,7 +2648,7 @@ def beamFromElement(elem, slurBundle=None):

**Attributes/Elements Implemented:**

- <clef>, <chord>, <note>, <rest>, <space>, <tuplet>, <beam>, <barLine>
- <clef>, <chord>, <note>, <rest>, <space>, <tuplet>, <beam>, <bTrem>, <barLine>

**Attributes/Elements Ignored:**

Expand Down Expand Up @@ -2660,7 +2676,7 @@ def beamFromElement(elem, slurBundle=None):

**Contained Elements not Implemented:**

- MEI.cmn: bTrem beatRpt fTrem halfmRpt meterSig meterSigGrp
- MEI.cmn: beatRpt fTrem halfmRpt meterSig meterSigGrp
- MEI.critapp: app
- MEI.edittrans: (all)
- MEI.mensural: ligature mensur proport
Expand All @@ -2677,6 +2693,7 @@ def beamFromElement(elem, slurBundle=None):
f'{MEI_NS}rest': restFromElement,
f'{MEI_NS}tuplet': tupletFromElement,
f'{MEI_NS}beam': beamFromElement,
f'{MEI_NS}bTrem': bTremFromElement,
f'{MEI_NS}space': spaceFromElement,
f'{MEI_NS}barLine': barLineFromElement,
}
Expand Down Expand Up @@ -2753,7 +2770,7 @@ def tupletFromElement(elem, slurBundle=None):

**Attributes/Elements Implemented:**

- <tuplet>, <beam>, <note>, <rest>, <chord>, <clef>, <space>, <barLine>
- <tuplet>, <beam>, <note>, <rest>, <chord>, <clef>, <bTrem>, <space>, <barLine>
- @num and @numbase

**Attributes/Elements in Testing:** none
Expand Down Expand Up @@ -2782,7 +2799,7 @@ def tupletFromElement(elem, slurBundle=None):

**Contained Elements not Implemented:**

- MEI.cmn: bTrem beatRpt fTrem halfmRpt meterSig meterSigGrp
- MEI.cmn: beatRpt fTrem halfmRpt meterSig meterSigGrp
- MEI.critapp: app
- MEI.edittrans: (all)
- MEI.mensural: ligature mensur proport
Expand All @@ -2796,6 +2813,7 @@ def tupletFromElement(elem, slurBundle=None):
f'{MEI_NS}rest': restFromElement,
f'{MEI_NS}chord': chordFromElement,
f'{MEI_NS}clef': clefFromElement,
f'{MEI_NS}bTrem': bTremFromElement,
f'{MEI_NS}space': spaceFromElement,
f'{MEI_NS}barLine': barLineFromElement,
}
Expand Down Expand Up @@ -2835,6 +2853,87 @@ def tupletFromElement(elem, slurBundle=None):
return tuple(tupletMembers)


def bTremFromElement(elem, slurBundle=None):
'''
<bTrem> A measured tremolo on a single note or chord (also called a bowed tremolo), in which
the enclosed note or chord is rapidly repeated in performance.

In MEI 2013 (MEI.cmn module).

:param elem: The ``<bTrem>`` element to process.
:type elem: :class:`~xml.etree.ElementTree.Element`
:returns: An iterable of the objects contained within the ``<bTrem>`` container. The wrapped
``<note>`` or ``<chord>`` is imported with its notated duration, so that the onsets of
following events are not shifted.
:rtype: list of :class:`~music21.base.Music21Object`

**Example**

A quarter-note chord notated as a measured tremolo of eighth notes (``@unitdur="8"``, one
tremolo mark). The function returns the chord itself, carrying its notated duration and a
:class:`~music21.expressions.Tremolo` expression.

>>> from xml.etree import ElementTree as ET
>>> meiSnippet = """<bTrem xmlns="http://www.music-encoding.org/ns/mei" unitdur="8">
... <chord dur="4">
... <note pname="E" oct="4"/>
... <note pname="E" oct="5"/>
... </chord>
... </bTrem>"""
>>> meiSnippet = ET.fromstring(meiSnippet)
>>> result = mei.base.bTremFromElement(meiSnippet)
>>> len(result)
1
>>> result[0]
<music21.chord.Chord E4 E5>
>>> result[0].quarterLength
1.0
>>> result[0].expressions
[<music21.expressions.Tremolo>]
>>> result[0].expressions[0].numberOfMarks
1

**Attributes/Elements Implemented:**

- <note>, <chord>
- @unitdur (mapped to :attr:`~music21.expressions.Tremolo.numberOfMarks`)

**Attributes/Elements in Testing:** none

**Attributes not Implemented:**

- att.common (@label, @n, @xml:base) (att.id (@xml:id))
- att.typography (@fontfam, @fontname, @fontsize, @fontstyle, @fontweight)
- att.bTrem.log (att.tremmeasured (@num, @numbase))
- att.bTrem.vis (all)
- att.bTrem.ges (att.duration.performed (@dur.ges))
- att.bTrem.anl (all)

**Contained Elements not Implemented:** none
'''
# mapping from tag name to our converter function
tagToFunction = {
f'{MEI_NS}chord': chordFromElement,
f'{MEI_NS}note': noteFromElement,
}

# Import the wrapped <note>/<chord> as an ordinary note/chord so its notated duration survives;
# otherwise the tremolo (and every onset after it in the layer) would be silently dropped.
tremoloStuff = _processEmbeddedElements(elem.findall('*'), tagToFunction, elem.tag, slurBundle)

# Attach a measured Tremolo, deriving the number of marks from @unitdur when it is a usable
# duration; timing correctness is preserved even when @unitdur is absent or unrecognized.
numberOfMarks = _MEI_UNITDUR_TO_TREMOLO_MARKS.get(elem.get('unitdur', ''))
if numberOfMarks is not None:
for eachObj in tremoloStuff:
if isinstance(eachObj, note.NotRest):
tremolo = expressions.Tremolo()
tremolo.numberOfMarks = numberOfMarks
eachObj.expressions.append(tremolo)

return tremoloStuff


def layerFromElement(elem, overrideN=None, slurBundle=None):
'''
<layer> An independent stream of events on a staff.
Expand All @@ -2860,7 +2959,7 @@ def layerFromElement(elem, overrideN=None, slurBundle=None):

**Attributes/Elements Implemented:**

- <clef>, <chord>, <note>, <rest>, <mRest>, <beam>, <tuplet>, <space>, <mSpace> , and
- <clef>, <chord>, <note>, <rest>, <mRest>, <beam>, <tuplet>, <bTrem>, <space>, <mSpace> , and
<barLine> contained within
- @n, from att.common

Expand All @@ -2881,7 +2980,7 @@ def layerFromElement(elem, overrideN=None, slurBundle=None):

**Contained Elements not Implemented:**

- MEI.cmn: arpeg bTrem beamSpan beatRpt bend breath fTrem fermata gliss hairpin halfmRpt
- MEI.cmn: arpeg beamSpan beatRpt bend breath fTrem fermata gliss hairpin halfmRpt
harpPedal mRpt mRpt2 meterSig meterSigGrp multiRest multiRpt octave pedal
reh slur tie tuplet tupletSpan
- MEI.cmnOrnaments: mordent trill turn
Expand All @@ -2906,6 +3005,7 @@ def layerFromElement(elem, overrideN=None, slurBundle=None):
f'{MEI_NS}mRest': mRestFromElement,
f'{MEI_NS}beam': beamFromElement,
f'{MEI_NS}tuplet': tupletFromElement,
f'{MEI_NS}bTrem': bTremFromElement,
f'{MEI_NS}space': spaceFromElement,
f'{MEI_NS}mSpace': mSpaceFromElement,
f'{MEI_NS}barLine': barLineFromElement,
Expand Down
59 changes: 59 additions & 0 deletions music21/mei/test_base.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@
from music21 import bar
from music21 import clef
from music21 import duration
from music21 import expressions
from music21 import instrument
from music21 import interval
from music21 import key
Expand Down Expand Up @@ -2223,6 +2224,64 @@ def testIntegration1cLayerFromElement(self):
except base.MeiAttributeError as maError:
self.assertEqual(base._MISSING_VOICE_ID, maError.args[0])

# -----------------------------------------------------------------------------
# Tests for bTremFromElement()

def testIntegration1BTremFromElement(self):
'''
bTremFromElement(): the wrapped <chord> is imported with its notated duration, and a
Tremolo expression is attached with the number of marks derived from @unitdur.
'''
inputXML = '''<bTrem xmlns="http://www.music-encoding.org/ns/mei" form="meas" unitdur="8">
<chord dur="4">
<note pname="E" oct="4" />
<note pname="E" oct="5" />
</chord>
</bTrem>'''
elem = ETree.fromstring(inputXML)

actual = base.bTremFromElement(elem)

self.assertIsInstance(actual, list)
self.assertEqual(1, len(actual))
self.assertEqual(1.0, actual[0].quarterLength)
self.assertEqual(['E4', 'E5'], [p.nameWithOctave for p in actual[0].pitches])
self.assertEqual(1, len(actual[0].expressions))
self.assertIsInstance(actual[0].expressions[0], expressions.Tremolo)
self.assertEqual(1, actual[0].expressions[0].numberOfMarks)

def testIntegration2BTremFromElement(self):
'''
bTremFromElement() within a <layer>: a <bTrem> must not be silently dropped. The tremolo
note/chord contributes its notated duration so the onsets of following events do not shift
(regression test for https://github.com/cuthbertLab/music21/issues/1994).
'''
inputXML = '''<layer n="1" xmlns="http://www.music-encoding.org/ns/mei">
<note xml:id="n1" dur="4" oct="4" pname="c" />
<bTrem xml:id="bt1" form="meas" unitdur="8">
<chord xml:id="ch1" dur="4">
<note xml:id="n2" oct="4" pname="e" />
<note xml:id="n3" oct="5" pname="e" />
</chord>
</bTrem>
<note xml:id="n4" dur="2" oct="4" pname="g" />
</layer>'''
elem = ETree.fromstring(inputXML)

actual = base.layerFromElement(elem)

self.assertEqual(3, len(actual))
# onsets are not shifted: the tremolo chord keeps its place on beat 2
self.assertEqual([0.0, 1.0, 2.0], [obj.offset for obj in actual])
self.assertEqual([1.0, 1.0, 2.0], [obj.quarterLength for obj in actual])
self.assertEqual('C4', actual[0].nameWithOctave)
# the beat-2 element is the E4/E5 chord, imported with a Tremolo expression
self.assertEqual(['E4', 'E5'], [p.nameWithOctave for p in actual[1].pitches])
self.assertEqual(1, len(actual[1].expressions))
self.assertIsInstance(actual[1].expressions[0], expressions.Tremolo)
self.assertEqual(1, actual[1].expressions[0].numberOfMarks)
self.assertEqual('G4', actual[2].nameWithOctave)

# -----------------------------------------------------------------------------
# Tests for staffFromElement()

Expand Down
Loading