music21.derivation

This module defines objects for tracking the derivation of one Stream from another.

Functions

music21.derivation.derivationMethod(function)

Derivation

class music21.derivation.Derivation(client=None)

A Derivation object keeps track of which Streams (or perhaps other Music21Objects) a Stream has come from and how.

>>> s1 = stream.Stream()
>>> s1.id = "DerivedStream"
>>> d1 = derivation.Derivation(s1)

>>> s2 = stream.Stream()
>>> s2.id = "OriginalStream"

>>> d1.method = 'manual'
>>> d1.origin = s2
>>> d1
<Derivation of <music21.stream.Stream DerivedStream> from <music21.stream.Stream OriginalStream> via "manual">
>>> d1.origin is s2
True

>>> d1.client is s1
True

>>> import copy
>>> d2 = copy.deepcopy(d1)
>>> d2.origin is s2
True

>>> d1.method = 'measure'
>>> d1.method
'measure'

Deleting the origin stream does not change the Derivation, since origin is held by strong ref:

>>> import gc  # Garbage collection...
>>> del(s2)
>>> unused = gc.collect()  # ensure Garbage collection is run
>>> d1
<Derivation of <music21.stream.Stream DerivedStream> from <music21.stream.Stream OriginalStream> via "measure">

But deleting the client stream changes the Derivation, since client is held by weak ref:

>>> del(s1)
>>> unused = gc.collect()  # ensure Garbage collection is run
>>> d1
<Derivation of None from <music21.stream.Stream OriginalStream> via "measure">

Derivation bases

• SlottedObject

Derivation read-only properties

Derivation.rootDerivation

Return a reference to the oldest source of this Stream; that is, chain calls to derivesFrom until we get to a Stream that cannot be further derived.

>>> s1 = stream.Stream()
>>> s1.repeatAppend(note.Note(), 10)
>>> s1.repeatAppend(note.Rest(), 10)
>>> s2 = s1.getElementsByClass('GeneralNote')
>>> s3 = s2.getElementsByClass('Note')
>>> s3.derivation.rootDerivation is s1
True

Derivation read/write properties

Derivation.client

Derivation.method

Returns the string of the method that was used to generate this Stream.

>>> s = stream.Stream()
>>> s.derivation.method is None
True

>>> sNotes = s.notes
>>> sNotes.derivation.method
'notes'

Derivation.origin

Derivation methods

Derivation.chain()

Iterator.

Returns Streams that this Derivation’s client Stream was derived from. This provides a way to obtain all Streams that the client passed through, such as those created by getElementsByClass() or flat.

>>> s1 = stream.Stream()
>>> s1.id = 's1'
>>> s1.repeatAppend(note.Note(), 10)
>>> s1.repeatAppend(note.Rest(), 10)
>>> s2 = s1.getElementsByClass('GeneralNote')
>>> s2.id = 's2'
>>> s3 = s2.getElementsByClass('Note')
>>> s3.id = 's3'
>>> for y in s3.derivation.chain():
...     print(y)
<music21.stream.Stream s2>
<music21.stream.Stream s1>

>>> list(s3.derivation.chain()) == [s2, s1]
True