Observer pattern for functions and bound methods
observed allows you to to sign up functions or methods to “observe” other functions or methods:
from observed import event @event 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:
from observed import event class Foo(object): def __init__(self, name): self.name = name @event def bar(self, arg): print("Object %s invoked bar with arg='%s'"%(self.name,arg)) def callback(arg): print("callback was invoked with arg='%s'"%(arg,)) a = Foo('a') b = Foo('b') # Sign up b.bar and callback to "observe" a.bar a.bar.add_observer(b.bar) a.bar.add_observer(callback) # Now when we call a.bar, b.bar and callback will be invoked with # the same arguments a.bar('baz') >>> Object a invoked bar with arg='baz' >>> Object b invoked bar with arg='baz' >>> callback was invoked with arg='baz'
This example is included in ./observed/example.py.
You can ask that the observed object pass itself as the first argument whenever it calls observers:
from observed import event @event 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
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.
- The @event 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.
- Tests included :)
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.
See the file NEWS for the user-visible changes from previous releases.
observed is free (as in beer) software. See the LICENSE file.
observed can be obtained from the python package index
or via git
Basic usage is illustrated at the top of this file. Further examples are given in ./observed/example.py
The source code is documented. Docstrings are required in contributions.
observed development is hosted on github. The current working repository is given in the Downloading section above.
Please submit bug tickets on the github tracking system