Metadata-Version: 2.4
Name: cs-obj
Version: 20260912
Summary: Convenience facilities for objects.
Keywords: python2,python3
Author-email: Cameron Simpson <cs@cskk.id.au>
Description-Content-Type: text/markdown
Classifier: Programming Language :: Python
Classifier: Programming Language :: Python :: 3
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: Operating System :: OS Independent
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Classifier: License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)
Requires-Dist: cs.context>=20250528
Requires-Dist: cs.deco>=20260912
Requires-Dist: cs.seq>=20260912
Project-URL: MonoRepo Commits, https://bitbucket.org/cameron_simpson/css/commits/branch/main
Project-URL: Monorepo Git Mirror, https://github.com/cameron-simpson/css
Project-URL: Monorepo Hg/Mercurial Mirror, https://hg.sr.ht/~cameron-simpson/css
Project-URL: Source, https://github.com/cameron-simpson/css/blob/main/lib/python/cs/obj.py

Convenience facilities for objects.

*Latest release 20260912*:
* New NoAttrs leaf mixin to allow classes to freely use super().__getattr__ and to issue a more informative AttributeError.
* Refreshable: new refresh_related1() method for related objects to be refreshed but not recursively.
* Refreshable: use self.refresh_lock as a mutex if present.
* Refreshable: pass the related() and related1() items through not_none to accomodate these meethods returning some Nones, which is often expedient.
* Refreshable.{refresh,_refresh}: drop the optional resource parameter, turned out to be unused.



Short summary:


* `as_dict`: Return a dictionary with keys mapping to the values of the attributes of `o`.


* `copy`: Convenient function to shallow copy an object with simple modifications.


* `flavour`: Return constants indicating the ``flavour'' of an object: * `T_MAP`: DictType, DictionaryType, objects with an __keys__ or keys attribute. * `T_SEQ`: TupleType, ListType, objects with an __iter__ attribute. * `T_SCALAR`: Anything else.


* `NoAttrs`: A stub class whose `__getattr__` raises `AttributeError`. This exists to be put at the end of the subclasses for concrete nonmixin classes which have multiple `__getattr__` methods in their MRO, so that they can always call `super().__getattr__`.


* `O`: The `O` class is now obsolete, please subclass `types.SimpleNamespace` or use a dataclass.


* `O_attritems`: Generator yielding `(attr,value)` for relevant attributes of `o`.


* `O_attrs`: Yield attribute names from `o` which are pertinent to `O_str`.


* `O_merge`: Merge key:value pairs from a mapping into an object.


* `O_str`: Return a `str` representation of the object `o`.


* `obj_as_dict`: OBSOLETE version of obj_as_dict, suggestion: use cs.obj.as_dict.


* `Proxy`: An extremely simple proxy object that passes all unmatched attribute accesses to the proxied object.


* `public_subclasses`: Return a set of the subclasses of `cls` which have public names.


* `Refreshable`: A mixin for refreshable objects. The object must provide a `_refresh()` method, returning `True` if the object was updated and false otherwise.


* `Sentinel`: A simple class for named sentinels whose `str()` is just the name and whose `==` uses `is`.


* `singleton`: Obtain an object for `key` via `registry` (a mapping of `key`=>object). Return `(is_new,object)`.


* `SingletonMixin`: A mixin turning a subclass into a singleton factory.


* `TrackedClassMixin`: A mixin to track all instances of a particular class.

# Functions

## O_attritems(o)

Generator yielding `(attr,value)` for relevant attributes of `o`.

## O_attrs(o)

Yield attribute names from `o` which are pertinent to `O_str`.

Note: this calls `getattr(o,attr)` to inspect it in order to
prune callables.

## O_merge(o, _conflict=None, _overwrite=False, **kw)

Merge key:value pairs from a mapping into an object.

Ignore keys that do not start with a letter.
New attributes or attributes whose values compare equal are
merged in. Unequal values are passed to:

    _conflict(o, attr, old_value, new_value)

to resolve the conflict. If _conflict is omitted or None
then the new value overwrites the old if _overwrite is true.

## O_str(o, no_recurse=False, seen=None)

Return a `str` representation of the object `o`.

Parameters:
* `o`: the object to describe.
* `no_recurse`: if true, do not recurse into the object's structure.
  Default: `False`.
* `seen`: a set of previously sighted objects
  to prevent recursion loops.

## as_dict(o, selector=None)

Return a dictionary with keys mapping to the values of the attributes of `o`.

Parameters:
* `o`: the object to map
* `selector`: the optional selection criterion

If `selector` is omitted or `None`, select "public" attributes,
those not commencing with an underscore.

If `selector` is a `str`, select attributes starting with `selector`.

Otherwise presume `selector` is callable
and select attributes `attr` where `selector(attr)` is true.

## copy(obj, **kw)

Convenient function to shallow copy an object with simple modifications.

Performs a shallow copy of `self` using `copy.copy`.

Treat all keyword arguments as `(attribute,value)` 2-tuples and
replace those attributes with the supplied values.

## flavour(obj)

Return constants indicating the ``flavour'' of an object:
* `T_MAP`: DictType, DictionaryType, objects with an __keys__ or keys attribute.
* `T_SEQ`: TupleType, ListType, objects with an __iter__ attribute.
* `T_SCALAR`: Anything else.

## obj_as_dict(o, **kw)

OBSOLETE version of obj_as_dict, suggestion: use cs.obj.as_dict

OBSOLETE convesion of an object to a `dict`. Please us `cs.obj.as_dict`.

## public_subclasses(cls, extras=())

Return a set of the subclasses of `cls` which have public names.

## singleton(registry, key, factory, fargs, fkwargs)

Obtain an object for `key` via `registry` (a mapping of `key`=>object).
Return `(is_new,object)`.

If the `key` exists in the registry, return the associated object.
Otherwise create a new object by calling `factory(*fargs,**fkwargs)`
and store it as `key` in the `registry`.

The `registry` may be any mapping of `key`s to objects
but will usually be a `weakref.WeakValueDictionary`
in order that object references expire as normal,
allowing garbage collection.

*Note*: this function *is not* thread safe.
Multithreaded users should hold a mutex.

See the `SingletonMixin` class for a simple mixin to create
singleton classes,
which does provide thread safe operations.

# Classes

## class NoAttrs

A stub class whose `__getattr__` raises `AttributeError`.
This exists to be put at the end of the subclasses for concrete
nonmixin classes which have multiple `__getattr__` methods
in their MRO, so that they can always call `super().__getattr__`.

This exists because `object` has no `__getattr__`, necessitating
this ugly shuffle in mixin `__getattr__` methods:

    def __getattr__(self, attr):
        ... return the mixin's special attr ...
        try:
            gsa = super().__getattr__
        except AttributeError:
            raise AttributeError(f'{self.__class__.__name__}.{attr}')
        else:
            return gsa(attr)

With `NoAttrs` at the end of the MRO every mixin's `__geattr__` can be:

    def __getattr__(self, attr):
        ... return the mixin's special attr ...
        return super().__getattr__(attr)

A concrete class is then defined as:

    class C(AMixin,BMixin,NoAttrs):

Because of Python's MRO construction rules, a subclass like:

    class D(C,DMixin,NoAttrs):

still places `NoAttrs` at the end of the MRO, producing correct behaviour.

`NoAttrs.__getattr__` issues a warning if `super().__getattr__` actually exists.

#e## NoAttrs.__dict__

Read-only proxy of a mapping.

#e## NoAttrs.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

### NoAttrs.__getattr__(self, attr)

Just raise `AttributeError` with a nice mesage.

#e## NoAttrs.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

## class O(types.SimpleNamespace)

The `O` class is now obsolete, please subclass `types.SimpleNamespace`
or use a dataclass.

#e## O.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## O.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

#e## O.callers

Build an unordered collection of unique elements.

## class Proxy

An extremely simple proxy object
that passes all unmatched attribute accesses to the proxied object.

Note that setattr and delattr work directly on the proxy, not the proxied object.

#e## Proxy.__dict__

Read-only proxy of a mapping.

#e## Proxy.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## Proxy.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

## class Refreshable

A mixin for refreshable objects.
The object must provide a `_refresh()` method, returning
`True` if the object was updated and false otherwise.

This mixin provides a `.refresh()` method which implements the refresh logic
and various related `refresh_*` methods/properties.

#e## Refreshable.REFRESH_LIFESPAN

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## Refreshable.REFRESH_RATELIMIT

Convert a string or number to a floating-point number, if possible.

#e## Refreshable.__dict__

Read-only proxy of a mapping.

#e## Refreshable.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## Refreshable.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

### Refreshable.refresh(self, *, data=None, force=False, lifespan: float | None = None, map=<class 'map'>, ratelimit: float | None = None, recurse=False, seen=None, **_refresh_kw) -> bool

Refresh this object; if it is stale attempt to refresh via `self._refresh()`.
Return `True` if the object was updated, `False` otherwise.

Note that this returns `False` if the object was considered
still current; `False` is not an error.

The refresh policy is: if `force` or (the object's information
is stale and the rate limit does not preclude a refresh),
call `self._refresh()`.
This is measured by `self.refresh_needed()`.

State about the refresh poll times is kept in
`self.refresh_last_poll` and `self.refresh_last_update`.

Keyword parameters:
* `data`: optional object providing the refresh data,
  passed to `self._refresh()` as the `data` keyword argument;
  if not `None` then `_refresh` is always called and should
  apply it instead of making whatever API call or other
  action it would perform passed to `self._refresh()
* `force`: optional flag, default `False`; if true attempt
  a refresh regardless of staleness or the rate limit
* `lifespan`: how many seconds before updated information
  is considered no stale, default from `self.refresh_lifespan`,
  or `type(self).REFRESH_RATELIMIT`
* `map`: optional `map()`-like function to call
  refresh on the related objects; this hook exists to allow
  for example APIs to pass in a curried `pmap()` call to
  refresh some objects in parallel; the default map function is `map()`
* `ratelimit`: how many seconds should elapsed before
  attempting a refresh, default from `self.refresh_ratelimit`
  or `type(self).REFRESH_RATELIMIT`
* `recurse`: optional flag, default `False`; if true then
  refresh the objects from `self.refresh_related1()` nonrecursively
  and recursively refresh the objects from `self.refresh_related()`
* `seen`: optional set of keys to prevent unbound recursion

Other keyword parameters are passed to `self._refresh()` if it is called.

Note the two related-object methods, `refresh_related()`
and `refresh_related1()`.  These exist to allow a recursive
refresh to refresh "descendant" objects recursively and
other related "adjacent" or "superior" objects nonrecursively.

Supposing you're refreshing a section topic in a news site;
you might recursively refresh all the articles in the topic
and the authors of the articles. However you likely also
want to refresh other objects related to the topic, perhaps
the table of topics and other things; recursing into those
objects might refresh everything on the entire site.
Accordingly the descendant objects would be enumerated by
`refresh_related()` and the adjacent/superior objects by
`refresh_related1()`.

Note that because a `recurse=True` call descends a potentially
arbitrary tree of related objects, if `map` is supplied as,
for example, `pmap`, that should be a curried call with a
shared `Semaphore` to control the concurrency, such as
`partial(pmap,concurrent=Semaphore(4))`.

It is probably a mistake to call this with non-`None` `data`
and `recurse` true. It will be accepts and the `data` applied
to `self` and the recursion done without `data`.
(Now we raise `ValueError` for this.)

### Refreshable.refresh_key(self)

Return the key value for the `seen` set used in a recursive refresh.
This default returns `id(self)`; classes like `Entity`
would use a characteristic value like `self.name`.

### Refreshable.refresh_needed(self, *, lifespan: float | None = None, now: float | None = None) -> bool

Test whether `self` is considered stale.

Parameters:
* `lifespan`: how many seconds before updated information
  is considered no stale, default from `self.refresh_lifespan`,
  or `type(self).REFRESH_LIFESPAN`
 * `now`: optional reference time, default from `time.time()`

### Refreshable.refresh_related(self) -> Iterable

Return the related objects which should also be refreshed in recursive refreshes.

### Refreshable.refresh_related1(self) -> Iterable

Return the related objects which should also be refreshed
in recursive refreshes, but nonrecursively.

### Refreshable.refreshed(self, **refresh_kw)

A variant on `refresh()` which returns `self` to support chaining.
This isn't the default because that's not Pythonic.

## class Sentinel

A simple class for named sentinels whose `str()` is just the name
and whose `==` uses `is`.

Example:

    >>> from cs.obj import Sentinel
    >>> MISSING = Sentinel("MISSING")
    >>> print(MISSING)
    MISSING
    >>> other = Sentinel("other")
    >>> MISSING == other
    False
    >>> MISSING == MISSING
    True

#e## Sentinel.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## Sentinel.__hash__

The type of the None singleton.

#e## Sentinel.__slots__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

#e## Sentinel.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

## class SingletonMixin

A mixin turning a subclass into a singleton factory.

*Note*: this mixin overrides `object.__new__`
and may not play well with other classes which override `__new__`.

*Warning*: because of the mechanics of `__new__`,
the instance's `__init__` method will always be called
after `__new__`,
even when a preexisting object is returned.
Therefore that method should be sensible
even for an already initialised
and probably subsequently modified object.

My suggested approach is to access some attribute,
and preemptively return if it already exists.
Example:

    def __init__(self, x, y):
        if 'x' in self.__dict__:
            return
        self.x = x
        self.y = y

*Note*: we probe `self.__dict__` above to accomodate classes
with a `__getattr__` method.

*Note*: each class registry has a lock,
which ensures that reuse of an object
in multiple threads will call the `__init__` method
in a thread safe serialised fashion.

Implementation requirements:
a subclass should:
* provide a method `_singleton_key(*args,**kwargs)`
  returning a key for use in the single registry,
  computed from the positional and keyword arguments
  supplied on instance creation
  i.e. those which `__init__` would normally receive.
  This should have the same signature as `__init__`
  but using `cls` instead of `self`.
* provide a normal `__init__` method
  which can be safely called again
  after some earlier initialisation.

This class is thread safe for the registry operations.

Example:

    class Pool(SingletonMixin):

        @classmethod
        def _singleton_key(cls, foo, bah=3):
            return foo, bah

        def __init__(self, foo, bah=3):
            if hasattr(self, 'foo'):
                return
           ... normal __init__ stuff here ...
           self.foo = foo
           ...

#e## SingletonMixin.__dict__

Read-only proxy of a mapping.

#e## SingletonMixin.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

### SingletonMixin.__hash__(self)

default hash and equality methods

#e## SingletonMixin.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

### SingletonMixin.singleton_also_by(also_key, key)

Obtain a singleton by a secondary key.
Return the instance or `None`.

Parameters:
* `also_key`: the name of the secondary key index
* `key`: the key for the index

## class TrackedClassMixin

A mixin to track all instances of a particular class.

This is aimed at checking the global state of objects of a
particular type, particularly states like counters. The
tracking is attached to the class itself.

The class to be tracked includes this mixin as a superclass and calls:

    TrackedClassMixin.__init__(class_to_track)

from its __init__ method. Note that `class_to_track` is
typically the class name itself, not `type(self)` which would
track the specific subclass. At some relevant point one can call:

    self.tcm_dump(class_to_track[, file])

`class_to_track` needs a `tcm_get_state` method to return the
salient information, such as this from cs.resources.MultiOpenMixin:

    def tcm_get_state(self):
        return {'opened': self.opened, 'opens': self._opens}

See cs.resources.MultiOpenMixin for example use.

#e## TrackedClassMixin.__dict__

Read-only proxy of a mapping.

#e## TrackedClassMixin.__firstlineno__

int([x]) -> integer
int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating-point
numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string,
bytes, or bytearray instance representing an integer literal in the
given base.  The literal can be preceded by '+' or '-' and be surrounded
by whitespace.  The base defaults to 10.  Valid bases are 0 and 2-36.
Base 0 means to interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4

#e## TrackedClassMixin.__static_attributes__

Built-in immutable sequence.

If no argument is given, the constructor returns an empty tuple.
If iterable is specified the tuple is initialized from iterable's items.

If the argument is a tuple, the return value is the same object.

### TrackedClassMixin.tcm_all_state(klass)

Generator yielding tracking information
for objects of type `klass`
in the form `(o,state)`
where `o` if a tracked object
and `state` is the object's `get_tcm_state` method result.

### TrackedClassMixin.tcm_dump(klass, f=None)

Dump the tracking information for `klass` to the file `f`
(default `sys.stderr`).

# Release Log



*Release 20260912*:
* New NoAttrs leaf mixin to allow classes to freely use super().__getattr__ and to issue a more informative AttributeError.
* Refreshable: new refresh_related1() method for related objects to be refreshed but not recursively.
* Refreshable: use self.refresh_lock as a mutex if present.
* Refreshable: pass the related() and related1() items through not_none to accomodate these meethods returning some Nones, which is often expedient.
* Refreshable.{refresh,_refresh}: drop the optional resource parameter, turned out to be unused.

*Release 20260610*:
* Refreshable._refresh: this method must now accept an optional `data=` parameter which will be used to update the entity instead of consulting the original source.
* Refrehable.refresh: new map parameter to specify a function instead of map for the recursion, such as pmap().
* Refreshable.refreshed: change the meaning of `.refreshd()` to be self after a `.refresh()`, supporting chaining.

*Release 20260526*:
Refreshable mixin class embodying refresh logic.

*Release 20250306*:
* Remove cs.py3 dependency, this module has not worked in python2 for quite a while.
* copy: drop use of positional parameters.

*Release 20250103*:
public_subclasses: new optional extras= parameter for additional classes to scan, now returns a set.

*Release 20241009*:
public_subclasses: catch TypeError from "type.__subclasses__", which is just a function.

*Release 20241005*:
New public_subclasses(cls) returning all subclasses with public names.

*Release 20220918*:
* SingletonMixin: change example to probe self__dict__ instead of hasattr, faster and less fragile.
* New Sentinel class for named sentinel objects, equal only to their own instance.

*Release 20220530*:
SingletonMixin: add default __hash__ and __eq__ methods to support dict and set membership.

*Release 20210717*:
SingletonMixin: if cls._singleton_key returns None we always make a new instance and do not register it.

*Release 20210306*:
SingletonMixin: make singleton_also_by() a public method.

*Release 20210131*:
SingletonMixin: new _singleton_also_indexmap method to return a mapping of secondary keys to values to secondary lookup, _singleton_also_index() to update these indices, _singleton_also_by to look up a secondary index.

*Release 20210122*:
SingletonMixin: new _singleton_instances() method returning a list of the current instances.

*Release 20201227*:
SingletonMixin: correctly invoke __new__, a surprisingly fiddly task to get right.

*Release 20201021*:
* @OBSOLETE(obj_as_dict), recommend "as_dict()".
* [BREAKING] change as_dict() to accept a single optional selector instead of various mutually exclusive keywords.

*Release 20200716*:
SingletonMixin: no longer require special _singleton_init method, reuse default __init__ implicitly through __new__ mechanics.

*Release 20200517*:
Documentation improvements.

*Release 20200318*:
* Replace obsolete O class with a new subclass of SimpleNamespace which issues a warning.
* New singleton() generic factory function and SingletonMixin mixin class for making singleton classes.

*Release 20190103*:
* New mixin class TrackedClassMixin to track all instances of a particular class.
* Documentation updates.

*Release 20170904*:
Minor cleanups.

*Release 20160828*:
* Use "install_requires" instead of "requires" in DISTINFO.
* Minor tweaks.

*Release 20150118*:
move long_description into cs/README-obj.rst

*Release 20150110*:
cleaned out some old junk, readied metadata for PyPI
