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Extracting information from Musicxml

I am new to programming and Python, but a lot of my current research is about extracting data from musicxml files. I have music and want to extract the number of accidents that occur in a piece that is not part of the key signature. I have no idea how to do this, please can anyone help? Here is an example of one measure from the musicxml file I'm looking at:

<measure number='19'>
        <print new-system='no'/>
        <note>
            <rest/>
            <duration>768</duration>
            <voice>1</voice>
            <type>quarter</type>
            <staff>1</staff>
        </note>
        <backup>
            <duration>768</duration>
        </backup>
        <note>
            <pitch>
                <step>E</step>
                <octave>4</octave>
            </pitch>
            <duration>2304</duration>
            <tie type='start'/>
            <voice>2</voice>
            <type>half</type>
            <dot/>
            <staff>1</staff>
            <notations>
                <tied type='start'/>
                <slur type='stop' number='1'/>
            </notations>
        </note>
        <backup>
            <duration>1536</duration>
        </backup>
        <note>
            <pitch>
                <step>E</step>
                <alter>3</alter>
                <octave>3</octave>
            </pitch>
            <duration>1536</duration>
            <voice>1</voice>
            <type>half</type>
            <staff>1</staff>
        </note>
        <note>
            <chord/>
            <pitch>
                <step>G</step>
                <alter>4</alter>
                <octave>3</octave>
            </pitch>
            <duration>1536</duration>
            <voice>1</voice>
            <type>half</type>
            <staff>1</staff>
        </note>
        <backup>
            <duration>2304</duration>
        </backup>
        <note>
            <pitch>
                <step>E</step>
                <octave>2</octave>
            </pitch>
            <duration>2304</duration>
            <voice>5</voice>
            <type>half</type>
            <dot/>
            <staff>2</staff>
        </note>
    </measure>

The problem translates into searching through the musicxml file and counting the number of times

<pitch>
   <step>*</step>
   <alter>**</alter>
       ...

occurs when * is not (F or C), and also finding the number of times that * is F or C, and it is not followed by a tag <alter>.

Any help or advice would be greatly appreciated!

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2 answers

Python, , MusicXML:

1) , alter. alter ; - , . ? , , MusicXML MusicXML.

2) Python, , MusicXML. , . music21, Python. http://web.mit.edu/music21/.

!

+4

python xml.dom , XML . -, javascript.

from xml.dom.minidom import parse, parseString

def get_step(note):
    stepNode = note.getElementsByTagName("step")[0]
    #get the text from the Text Node within the <step>,
    #and convert it from unicode to ascii
    return str(stepNode.childNodes[0].nodeValue)

def get_alter(note):
    alters = note.getElementsByTagName("alter")
    if len(alters) == 0:
        return None
    return alters[0]

def is_rest(note):
    return len(note.getElementsByTagName("rest")) > 0

def is_accidental(note):
    return get_alter(note) != None

dom = parse("data.xml")

notes = dom.getElementsByTagName("note")
#rests don't have steps or alters, so we don't care about them. Filter them out.
notes = filter(lambda note: not is_rest(note), notes)

#compile a list of notes of all accidentals (notes with <alter> tags)
accidentals = filter(is_accidental, notes)
#remove notes that are F or C
accidentals_that_are_not_f_or_c = filter(lambda note: get_step(note) not in ["F", "C"], accidentals)

#compile a list of notes that don't contain the alter tag
non_accidentals = filter(lambda note: not is_accidental(note), notes)
#remove notes that are not F or C
non_accidentals_that_are_f_or_c = filter(lambda note: get_step(note) in ["F", "C"], non_accidentals)

print "Accidental notes that are not F or C:"
if len(accidentals_that_are_not_f_or_c) == 0:
    print "(None found)"
else:
    for note in accidentals_that_are_not_f_or_c:
        print get_step(note)

print "Non-accidental notes that are F or C:"
if len(non_accidentals_that_are_f_or_c) == 0:
    print "(None found)"
else:
    for note in non_accidentals_that_are_f_or_c:
        print get_step(note), get_step(note) in ["F", "C"]

:

Accidental notes that are not F or C:
E
G
Non-accidental notes that are F or C:
(None found)
+2

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