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"""ZooKeeper Leader Elections
:Maintainer: None:Status: Unknown
"""
from kazoo.exceptions import CancelledError
class Election(object): """Kazoo Basic Leader Election
Example usage with a :class:`~kazoo.client.KazooClient` instance::
zk = KazooClient() zk.start() election = zk.Election("/electionpath", "my-identifier")
# blocks until the election is won, then calls # my_leader_function() election.run(my_leader_function)
"""
def __init__(self, client, path, identifier=None): """Create a Kazoo Leader Election
:param client: A :class:`~kazoo.client.KazooClient` instance. :param path: The election path to use. :param identifier: Name to use for this lock contender. This can be useful for querying to see who the current lock contenders are.
"""
self.lock = client.Lock(path, identifier)
def run(self, func, *args, **kwargs): """Contend for the leadership
This call will block until either this contender is cancelled or this contender wins the election and the provided leadership function subsequently returns or fails.
:param func: A function to be called if/when the election is won. :param args: Arguments to leadership function. :param kwargs: Keyword arguments to leadership function.
"""
if not callable(func): raise ValueError("leader function is not callable")
try: with self.lock: func(*args, **kwargs)
except CancelledError: pass
def cancel(self): """Cancel participation in the election
.. note::
If this contender has already been elected leader, this method will not interrupt the leadership function.
"""
self.lock.cancel()
def contenders(self): """Return an ordered list of the current contenders in the
election
.. note::
If the contenders did not set an identifier, it will appear as a blank string.
"""
return self.lock.contenders()
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