music21.key

This module defines objects for representing key signatures as well as key areas. The KeySignature is used in Measure objects for defining notated key signatures.

The Key object is a fuller representation not just of a key signature but also of the key of a region.

Functions

music21.key.convertKeyStringToMusic21KeyString(textString)

Utility function to change strings in the form of “Eb” to “E-” (for E-flat major) and leaves alone proper music21 strings (like “E-” or “f#”). A little bit complex because of parsing bb as B-flat minor and Bb as B-flat major.

>>> key.convertKeyStringToMusic21KeyString('Eb')
'E-'
>>> key.convertKeyStringToMusic21KeyString('f#')
'f#'
>>> key.convertKeyStringToMusic21KeyString('bb')
'b-'
>>> key.convertKeyStringToMusic21KeyString('Bb')
'B-'
>>> key.convertKeyStringToMusic21KeyString('b#')
'b#'
>>> key.convertKeyStringToMusic21KeyString('c')    
'c'
music21.key.pitchToSharps(value, mode=None)

Given a pitch or music21.pitch.Pitch object, return the number of sharps found in that mode.

The mode parameter can be ‘major’, ‘minor’, or most of the common church/jazz modes (‘dorian’, ‘mixolydian’, etc.) including Locrian.

If mode is omitted or not found, the default mode is major.

(extra points to anyone who can find the earliest reference to the Locrian mode in print. David Cohen and I (MSC) have been looking for this for years).

>>> key.pitchToSharps('c')
0
>>> key.pitchToSharps('c', 'minor')
-3
>>> key.pitchToSharps('a', 'minor')
0
>>> key.pitchToSharps('d')
2
>>> key.pitchToSharps('e-')
-3
>>> key.pitchToSharps('a')
3
>>> key.pitchToSharps('e', 'minor')
1
>>> key.pitchToSharps('f#', 'major')
6
>>> key.pitchToSharps('g-', 'major')
-6
>>> key.pitchToSharps('c#')
7
>>> key.pitchToSharps('g#')
8
>>> key.pitchToSharps('e', 'dorian')
2
>>> key.pitchToSharps('d', 'dorian')
0
>>> key.pitchToSharps('g', 'mixolydian')
0
>>> key.pitchToSharps('e-', 'lydian')
-2
>>> key.pitchToSharps('e-', 'lydian')
-2
>>> key.pitchToSharps('a', 'phrygian')
-1
>>> key.pitchToSharps('e', 'phrygian')
0
>>> key.pitchToSharps('f#')
6
>>> key.pitchToSharps('f-')
-8
>>> key.pitchToSharps('f--')
-15
>>> key.pitchToSharps('f--', 'locrian')
-20

But quarter tones don’t work:

>>> key.pitchToSharps('C~')
Traceback (most recent call last):
KeyException: Cannot determine sharps for quarter-tone keys! silly!
music21.key.sharpsToPitch(sharpCount)

Given a number a positive/negative number of sharps, return a Pitch object set to the appropriate major key value.

>>> key.sharpsToPitch(1)
<music21.pitch.Pitch G>
>>> key.sharpsToPitch(2)
<music21.pitch.Pitch D>
>>> key.sharpsToPitch(-2)
<music21.pitch.Pitch B->
>>> key.sharpsToPitch(-6)
<music21.pitch.Pitch G->

Note that these are music21.pitch.Pitch objects not just names:

>>> k1 = key.sharpsToPitch(6)
>>> k1
<music21.pitch.Pitch F#>
>>> k1.step
'F'
>>> k1.accidental
<accidental sharp>

KeySignature

class music21.key.KeySignature(sharps=None)

A KeySignature object specifies the signature to be used for a piece; it takes in zero, one, or two arguments. The only argument is an int giving the number of sharps, or if negative the number of flats.

If you are starting with the name of a key, see the Key object.

>>> A = key.KeySignature(3)
>>> A
<music21.key.KeySignature of 3 sharps>
>>> Eflat = key.KeySignature(-3)
>>> Eflat
<music21.key.KeySignature of 3 flats>

If you want to get a real Key, then use the Key object instead:

>>> illegal = key.KeySignature('c#')
Traceback (most recent call last):
KeySignatureException: Cannot get a KeySignature from this "number" of sharps: "c#"; 
    did you mean to use a key.Key() object instead?
>>> legal = key.Key('c#')
>>> legal.sharps
4
>>> legal
<music21.key.Key of c# minor>

KeySignature bases

KeySignature read-only properties

KeySignature.alteredPitches

Return a list of music21.pitch.Pitch objects that are altered by this KeySignature. That is, all Pitch objects that will receive an accidental.

>>> a = key.KeySignature(3)
>>> a.alteredPitches
[<music21.pitch.Pitch F#>, <music21.pitch.Pitch C#>, <music21.pitch.Pitch G#>]
>>> b = key.KeySignature(1)
>>> b.alteredPitches
[<music21.pitch.Pitch F#>]
>>> c = key.KeySignature(9)
>>> [str(p) for p in c.alteredPitches]
['F#', 'C#', 'G#', 'D#', 'A#', 'E#', 'B#', 'F##', 'C##']
>>> d = key.KeySignature(-3)
>>> d.alteredPitches
[<music21.pitch.Pitch B->, <music21.pitch.Pitch E->, <music21.pitch.Pitch A->]
>>> e = key.KeySignature(-1)
>>> e.alteredPitches
[<music21.pitch.Pitch B->]
>>> f = key.KeySignature(-6)
>>> [str(p) for p in f.alteredPitches]
['B-', 'E-', 'A-', 'D-', 'G-', 'C-']
>>> g = key.KeySignature(-8)
>>> [str(p) for p in g.alteredPitches]
['B-', 'E-', 'A-', 'D-', 'G-', 'C-', 'F-', 'B--']

Read-only properties inherited from Music21Object:

KeySignature read/write properties

KeySignature.sharps

Get or set the number of sharps. If the number is negative then it sets the number of flats. Equivalent to musicxml’s ‘fifths’ attribute.

>>> ks1 = key.KeySignature(2)
>>> ks1.sharps
2
>>> ks1.sharps = -4
>>> ks1
<music21.key.KeySignature of 4 flats>

Read/write properties inherited from Music21Object:

KeySignature methods

KeySignature.accidentalByStep(step)

Given a step (C, D, E, F, etc.) return the accidental for that note in this key (using the natural minor for minor) or None if there is none.

>>> g = key.KeySignature(1)
>>> g.accidentalByStep("F")
<accidental sharp>
>>> g.accidentalByStep("G")
>>> f = key.KeySignature(-1)
>>> bbNote = note.Note("B-5")
>>> f.accidentalByStep(bbNote.step)
<accidental flat>     

Fix a wrong note in F-major:

>>> wrongBNote = note.Note("B#4")
>>> if f.accidentalByStep(wrongBNote.step) != wrongBNote.pitch.accidental:
...    wrongBNote.pitch.accidental = f.accidentalByStep(wrongBNote.step)
>>> wrongBNote
<music21.note.Note B->

Set all notes to the correct notes for a key using the note’s Key Context. Before:

>>> s1 = stream.Stream()
>>> s1.append(key.KeySignature(4))  # E-major or C-sharp-minor
>>> s1.append(note.Note('C', type='half'))
>>> s1.append(note.Note('E-', type='half'))
>>> s1.append(key.KeySignature(-4)) # A-flat-major or F-minor
>>> s1.append(note.Note("A", type='whole'))
>>> s1.append(note.Note("F#", type='whole'))
>>> s1.show()
../_images/keyAccidentalByStep_Before.png

After:

>>> for n in s1.notes:
...    n.pitch.accidental = n.getContextByClass(key.KeySignature).accidentalByStep(n.step)
>>> s1.show()
../_images/keyAccidentalByStep.png
KeySignature.asKey(mode='major')

return a key.Key object representing this KeySignature object as a key in the given mode (default = major)

KeySignature.getScale(mode='major')

Return a music21.scale.Scale object (or, actually, a subclass such as MajorScale or MinorScale) that is representative of this key signature and mode.

Raises KeySignatureException if mode is not in [None, ‘major’, ‘minor’].

>>> ks = key.KeySignature(3)
>>> ks
<music21.key.KeySignature of 3 sharps>
>>> ks.getScale('major')
<music21.scale.MajorScale A major>
>>> ks.getScale('minor')
<music21.scale.MinorScale F# minor>
KeySignature.transpose(value, inPlace=False)

Transpose the KeySignature by the user-provided value. If the value is an integer, the transposition is treated in half steps. If the value is a string, any Interval string specification can be provided. Alternatively, a music21.interval.Interval object can be supplied.

>>> a = key.KeySignature(2)
>>> a
<music21.key.KeySignature of 2 sharps>
>>> a.asKey('major')
<music21.key.Key of D major>
>>> b = a.transpose('p5')
>>> b
<music21.key.KeySignature of 3 sharps>
>>> b.asKey('major')
<music21.key.Key of A major>
>>> b.sharps
3
>>> c = b.transpose('-m2')
>>> c.asKey('major')
<music21.key.Key of G# major>
>>> c.sharps
8
>>> d = c.transpose('-a3')
>>> d.asKey('major')
<music21.key.Key of E- major>
>>> d.sharps
-3

Transposition by semitone (or other chromatic interval)

>>> c = key.KeySignature(0)
>>> dflat = c.transpose(1)
>>> dflat
<music21.key.KeySignature of 5 flats>
>>> d = dflat.transpose(1)
>>> d
<music21.key.KeySignature of 2 sharps>
>>> eflat = d.transpose(1)
>>> eflat
<music21.key.KeySignature of 3 flats>

Methods inherited from Music21Object:

KeySignature instance variables

Instance variables inherited from Music21Object:

Key

class music21.key.Key(tonic=None, mode=None)

Note that a key is a sort of hypothetical/conceptual object. It probably has a scale (or scales) associated with it and a KeySignature, but not necessarily.

A Key object has all the attributes of a KeySignature and all the attributes of a DiatonicScale.

>>> cm = key.Key('c')  # lowercase = c minor.
>>> cm
<music21.key.Key of c minor>
>>> cm.mode
'minor'
>>> cm.tonic
<music21.pitch.Pitch C>
>>> cm.sharps
-3
>>> cm.pitchFromDegree(3)
<music21.pitch.Pitch E-4>
>>> cm.pitchFromDegree(7)
<music21.pitch.Pitch B-4>
>>> Csharpmaj = key.Key('C#') # uppercase = C# major
>>> Csharpmaj
<music21.key.Key of C# major>
>>> Csharpmaj.sharps
7
>>> Fflatmaj = key.Key('F-')
>>> Fflatmaj
<music21.key.Key of F- major>
>>> Fflatmaj.sharps
-8
>>> Fflatmaj.accidentalByStep('B')
<accidental double-flat>
>>> eDor = key.Key('E', 'dorian')
>>> eDor
<music21.key.Key of E dorian>
>>> eDor.sharps
2
>>> eDor.pitches
[<music21.pitch.Pitch E4>, 
 <music21.pitch.Pitch F#4>, 
 <music21.pitch.Pitch G4>, 
 <music21.pitch.Pitch A4>, 
 <music21.pitch.Pitch B4>, 
 <music21.pitch.Pitch C#5>, 
 <music21.pitch.Pitch D5>, 
 <music21.pitch.Pitch E5>]

Key bases

Key read-only properties

Key.parallel

if the Key is major or minor, return the parallel minor or major.

Otherwise, just returns self – this is the best way to not have random crashes in the middle of large datasets.

>>> k = key.Key('D')
>>> k
<music21.key.Key of D major>
>>> k.parallel
<music21.key.Key of d minor>
>>> k.parallel.parallel
<music21.key.Key of D major>
>>> key.Key('D', 'dorian').parallel
<music21.key.Key of D dorian>
Key.relative

if the Key is major or minor, return the relative minor or major.

Otherwise, just returns self – this is the best way to not have random crashes in the middle of large datasets.

Note that this uses .sharps as a speedup, so if that has been changed, there will be a problem...

>>> k = key.Key('E-')
>>> k
<music21.key.Key of E- major>
>>> k.relative
<music21.key.Key of c minor>
>>> k.relative.relative
<music21.key.Key of E- major>
>>> key.Key('D', 'dorian').relative
<music21.key.Key of D dorian>
Key.tonicPitchNameWithCase

Return the pitch name as a string with the proper case (upper = major; lower = minor)

Useful, but simple:

>>> k = key.Key("c#")
>>> k.tonicPitchNameWithCase
'c#'
>>> k = key.Key("B")
>>> k.tonicPitchNameWithCase
'B'
>>> k.mode = 'minor'
>>> k.tonicPitchNameWithCase
'b'

Read-only properties inherited from KeySignature:

Read-only properties inherited from ConcreteScale:

Read-only properties inherited from Music21Object:

Key read/write properties

Read/write properties inherited from KeySignature:

Read/write properties inherited from Music21Object:

Key methods

Key.tonalCertainty(method='correlationCoefficient', *args, **keywords)

Provide a measure of tonal ambiguity for Key determined with one of many methods.

The correlationCoefficient assumes that the alternateInterpretations list has been filled from the use of a KeyWeightKeyAnalysis subclass.

>>> littlePiece = converter.parse('tinyNotation: 4/4 c4 d e f g a b cc ee gg ee cc')
>>> k = littlePiece.analyze('key')
>>> k
<music21.key.Key of C major>
>>> k.tonalCertainty()
1.1648...

Three most likely alternateInterpretations:

>>> k.alternateInterpretations[0:3]
[<music21.key.Key of a minor>, <music21.key.Key of F major>, <music21.key.Key of d minor>]
>>> k.correlationCoefficient
0.9068...
>>> k.alternateInterpretations[0].correlationCoefficient
0.7778...

least likely interpretation:

>>> k.alternateInterpretations[-1]
<music21.key.Key of F# major>

Note that this method only exists if the key has come from an analysis method. Otherwise it raises a KeySignatureException

>>> k2 = key.Key('b-')
>>> k2.tonalCertainty()
Traceback (most recent call last):
KeySignatureException: cannot process ambiguity without a list of .alternateInterpretations
>>> k2.alternateInterpretations is None
True
Key.transpose(value, inPlace=False)

Transpose the Key by the user-provided value. If the value is an integer, the transposition is treated in half steps. If the value is a string, any Interval string specification can be provided. Alternatively, a music21.interval.Interval object can be supplied.

>>> dMajor = key.Key("D")
>>> dMajor
<music21.key.Key of D major>
>>> aMaj = dMajor.transpose('p5')
>>> aMaj
<music21.key.Key of A major>
>>> aMaj.sharps
3
>>> aMaj.tonic
<music21.pitch.Pitch A>
>>> aMaj.mode
'major'

inPlace works here

>>> changingKey = key.Key('g')
>>> changingKey
<music21.key.Key of g minor>
>>> changingKey.sharps
-2
>>> changingKey.transpose('m-3', inPlace=True)
>>> changingKey
<music21.key.Key of e minor>
>>> changingKey.sharps
1
>>> changingKey.transpose(1, inPlace=True)
>>> changingKey
<music21.key.Key of f minor>
>>> changingKey.sharps
-4
>>> changingKey.transpose(1, inPlace=True)
>>> changingKey
<music21.key.Key of f# minor>
>>> changingKey.transpose(1, inPlace=True)
>>> changingKey
<music21.key.Key of g minor>
>>> changingKey.transpose(1, inPlace=True)
>>> changingKey
<music21.key.Key of g# minor>

Methods inherited from KeySignature:

Methods inherited from DiatonicScale:

Methods inherited from ConcreteScale:

Methods inherited from Scale:

Methods inherited from Music21Object:

Key instance variables

Instance variables inherited from Music21Object: