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=================
Leader Election
=================
Each group can elect its own leader. There can be only one leader at a time
in a group. Only members that are running for the election can be elected.
As soon as one of leader steps down or dies, a new member that was running
for the election will be elected.
.. literalinclude:: ../../../../examples/leader_election.py
:language: python
The method
:meth:`tooz.coordination.CoordinationDriver.watch_elected_as_leader` allows
to register for a function to be called back when the member is elected as a
leader. Using this function indicates that the run is therefore running for
the election. The member can stop running by unregistering all its callbacks
with :meth:`tooz.coordination.CoordinationDriver.unwatch_elected_as_leader`.
It can also temporarily try to step down as a leader with
:meth:`tooz.coordination.CoordinationDriver.stand_down_group_leader`. If
another member is in the run for election, it may be elected instead.
To retrieve the leader of a group, even when not being part of the group,
the method :meth:`tooz.coordination.CoordinationDriver.get_leader()` can be
used.
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