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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, mode=None)

A KeySignature object specifies the signature to be used for a piece; it takes in zero, one, or two arguments. The first argument is an int giving the number of sharps, or if negative the number of flats. The second argument (deprecated – do not use) specifies the mode of the piece (‘major’, ‘minor’, or None for unknown).

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>

Some specification of mode can go into the KeySignature object:

>>> Eflat.mode = 'phrygian'
>>> Eflat
<music21.key.KeySignature of 3 flats, mode phrygian>

But 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--']
KeySignature.pitchAndMode

Returns a a two value list containing a music21.pitch.Pitch object that names this key and the value of mode.

The only applicable modes are ‘minor’ and all others (=Major)

>>> key.KeySignature(-7).pitchAndMode
(<music21.pitch.Pitch C->, None)
>>> key.KeySignature(-6).pitchAndMode
(<music21.pitch.Pitch G->, None)
>>> key.KeySignature(-3).pitchAndMode
(<music21.pitch.Pitch E->, None)
>>> key.KeySignature(0).pitchAndMode
(<music21.pitch.Pitch C>, None)
>>> key.KeySignature(1).pitchAndMode
(<music21.pitch.Pitch G>, None)
>>> csharp = key.KeySignature(4)
>>> csharp.mode = "minor"
>>> csharp.pitchAndMode
(<music21.pitch.Pitch C#>, 'minor')
>>> csharpPitch = csharp.pitchAndMode[0]
>>> csharpPitch.accidental
<accidental sharp>

Read-only properties inherited from Music21Object:

KeySignature read/write properties

KeySignature.mode

Get or set the mode.

Mode is supported in a very rough manner for KeySignature objects, but for more sophisticated use of modes use the Key object.

Mode may disappear in future releases so if you are counting on this for major or minor, consider supporting the Key object instead.

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’ feature

>>> 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.accidental:
...    wrongBNote.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.HalfNote("C"))
>>> s1.append(note.HalfNote("E-"))
>>> s1.append(key.KeySignature(-4)) # A-flat-major or F-minor
>>> s1.append(note.WholeNote("A"))
>>> s1.append(note.WholeNote("F#"))
>>> s1.show()
../_images/keyAccidentalByStep_Before.png

After:

>>> for n in s1.notes:
...    n.accidental = n.getContextByClass(key.KeySignature).accidentalByStep(n.step)
>>> s1.show()
../_images/keyAccidentalByStep.png
KeySignature.getScale()

Return a scale that is representative of this key signature and mode.

>>> ks = key.KeySignature(3)
>>> ks
<music21.key.KeySignature of 3 sharps>
>>> ks.getScale()
<music21.scale.MajorScale A major>
>>> ks.mode = 'minor'
>>> ks.getScale()
<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.pitchAndMode
(<music21.pitch.Pitch D>, None)
>>> b = a.transpose('p5')
>>> b
<music21.key.KeySignature of 3 sharps>
>>> b.pitchAndMode
(<music21.pitch.Pitch A>, None)
>>> b.sharps
3
>>> c = b.transpose('-m2')
>>> c.pitchAndMode
(<music21.pitch.Pitch G#>, None)
>>> c.sharps
8
>>> d = c.transpose('-a3')
>>> d.pitchAndMode
(<music21.pitch.Pitch E->, None)
>>> d.sharps
-3

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.

>>> cm = key.Key('c')  # cminor.
>>> cm
<music21.key.Key of c minor>
>>> cm.sharps
-3
>>> cm.pitchFromDegree(3)
<music21.pitch.Pitch E-4>
>>> cm.pitchFromDegree(7)
<music21.pitch.Pitch B-4>
>>> Csharpmaj = key.Key('C#')
>>> 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>

Key bases

Key read-only properties

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.

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

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 KeySignature:

  • isStream
  • hideObjectOnPrint
  • classSortOrder
  • groups
  • isVariant
  • id
  • isSpanner
  • xPosition

Instance variables inherited from DiatonicScale:

  • isStream
  • hideObjectOnPrint
  • classSortOrder
  • groups
  • isVariant
  • id
  • isSpanner
  • xPosition

Instance variables inherited from ConcreteScale:

  • isStream
  • hideObjectOnPrint
  • classSortOrder
  • groups
  • isVariant
  • id
  • isSpanner
  • xPosition

Instance variables inherited from Scale:

  • isStream
  • hideObjectOnPrint
  • classSortOrder
  • groups
  • isVariant
  • id
  • isSpanner
  • xPosition

Instance variables inherited from Music21Object: