observed 0.5.3
Observer pattern for functions and bound methods

**observed** allows you to to sign up functions or methods to "observe"
other functions or methods:

```python
from observed import observable_function

@observable_function
def observed_func(arg):
    print("observed_func: %s"%(arg,))

def observer_func(arg):
    print("observer_func: %s"%(arg,))

observed_func.add_observer(observer_func)
observed_func('banana')

>>> observed_func: banana
>>> observer_func: banana
```

You can also register observers for bound methods:

```python
from observed import observable_method

class Foo:
    def __init__(self, name):
        self.name = name

    @observable_method()
    def bar(self, arg):
        print("Object %s invoked bar with arg='%s'"%(self.name, arg))

    def baz(self, arg):
        print("Object %s invoked baz with arg='%s'"%(self.name, arg))

def callback(arg):
    print("callback was invoked with arg='%s'"%(arg,))

a = Foo('a')
b = Foo('b')
a.bar.add_observer(b.bar)
a.bar.add_observer(b.baz)
a.bar.add_observer(callback)
a.bar('banana')

>>> Object a invoked bar with arg='banana'
>>> Object b invoked bar with arg='banana'
>>> Object b invoked baz with arg='banana'
>>> callback was invoked with arg='banana'
```

You can ask that the observed object pass itself as the first argument
whenever it calls observers:

```python
from observed import observable_function

@observable_function
def observed_func():
    print("observed_func: I was called")

def observer_func(observed):
    print("observer_func: %s called me"%(observed.__name__,))

observed_func.add_observer(observer_func, identify_observed=True)
observed_func()

>>> observed_func: I was called
>>> observer_func: observed_func called me
```

When observed bound methods pass themselves as the observed object, keep in
mind that you can always access the associated instance via `__self__`:

```python
from observed import observable_method

class Foo:
    def __init__(self, name):
        self.name = name

    @observable_method()
    def bar(self):
        print("Object %s invoked bar"%(self.name,))

def callback(observed):
    print("callback was invoked by='%s'"%(observed.__self__.name,))

a = Foo('a')
a.bar.add_observer(callback, identify_observed=True)
a.bar()

>>> Object a invoked bar
>>> callback was invoked by a
```

Notable features include:

* A function or bound method is not kept alive just because it is
  observing something else. This is because the observed object does
  not keep any strong references to the observing objects. In CPython
  this means that your observers are automatically detached whenever the
  reference count to that observer goes to zero.

* The observable_method decorator can be used on methods in classes
  which are unhashable types, and can be used on an arbitrary number of
  methods in each class...

* ...but the descriptor which handles observable_method does not paste
  any data onto the instances it manages. There is zero chance of name
  collision on the observed instances.


## Installation

**observed** exists on the python package index, so you can do
`pip install observed` to install it. Alternatively, you can
download the source distribution and in the root directory of the
distribution do

```
$ python setup.py install
```


## News

See the file NEWS for the user-visible changes from previous releases.


## License

See `LICENSE.txt`.


## Downloading

observed can be obtained from the
[python package index at](https://pypi.python.org/pypi/observed)
or via [GitHub](https://github.com/DanielSank/observed.git).


## Documentation

Basic usage is illustrated at the top of this file. Further examples are
given in `example.py`.


## Development

observed development is hosted on github. The current working repository
is given in the Downloading section above.


## Bug Reporting

Please submit bug tickets on the
[GitHub tracking system](https://github.com/DanielSank/observed/issues).