Properties use decorators throughout

[mscuthbert]

short story - nearly all remaining x = property(_getX, _setX, doc=...) become @property def x / @x.setter.

Music21's been around for a while -- first supporting Python 2.2 which defined properties as:

def _getDuration(self):
    ...

def _setDuration(self, value):
    ...

duration = property(_getDuration, _setDuration, doc='''get or set Duration''')

Since all the way since Python 2.4 it's been possible to define properties as:

@property
def duration(self):
    '''get or set Duration'''
    ...

@duration.setter
def duration(self, value):
    ....

so when 2.4 became m21 minimum we started slowly using the second form. But music21 also uses doctests extensively. The problem was that while the old-style x = property(_get, _set) reported line numbers of failing doctests properly, the new-style @property did not. So debugging music21 was much harder with the new version. I pushed hard for a fix which finally as a Christmas 2023 present Serhiy Storchaka pushed through got a simpler solution into Python 3.13 (backported to 3.12.3 and 3.11.9) so it's finally available on basically all Python systems music21 runs on.

But like sitting asbestos, there was no need harm from old code so stirring up the pot and changing properties that already worked in music21 wasn't a priority. (Plus the new code is inelegant...note below.)

But in the past year or so, two things have changed:

1. agentic coding made this type of "almost-but-not-quite-simple-find-and-replace" so much easier.
2. type checking became so much more important, and mypy does not do as well with inferring types from property()

So it's worth a change. 60ish properties across 25 modules are refactored. Left along some places where the _get() or _set() form does double duty (such as having a second argument), and braille test's cool write-only properties.

Agent found 19 possible errors once mypy got their types. Mostly harmless (like setting stream.metadata = Metadata(); stream.metadata.title = ... getting a stream.metadata might be None) or type-only problems. (We did well there!)

AI-assisted (Claude)

Property ugliness

Not that anyone cares what I think, and probably too late/ship was sailed, unless we use a new term like @prop but the duplication of the function name in the setter is so ugly. Why not instead of

@property
def duration(self):
    '''get or set Duration'''
    ...

@duration.setter   # duration named here with funny syntax
def duration(self, value):  # and then named again here!
    ....

just do this:

@property
def duration(self):
    '''get or set Duration'''
    ...

@property
def duration(self, value):
    ....

And have in the basic case that one-argument = getter, and two-arguments = setter, and lookup is by matching name in the parsing. (The same type of magic as allowing super().__init__() instead of super(self, Duration).__init() in Py3)

Yes, there are some cases where you want to define just the setter alone or the thing you are setting has a different name etc. but there's a wonderful property() function for those strange cases!

[coveralls]

coverage: 93.331%. remained the same — property_to_decorator into master