openstack/deb-python-cassandra-driver
Code Issues Proposed changes

add HFPolicy docs to __init__

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This commit is contained in:
Jim Witschey
2017-06-07 16:14:00 -04:00
parent e9c99508cc
commit 2eaced282e
1 changed files with 12 additions and 5 deletions
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17
cassandra/policies.py
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@@ -461,11 +461,11 @@ class WhiteListRoundRobinPolicy(RoundRobinPolicy):
class HostFilterPolicy(LoadBalancingPolicy):
"""
A :class:`.LoadBalancingPolicy` subclass that takes an instantiated
``LoadBalancingPolicy`` as a child policy, and a single-argument predicate.
This policy defers to the child policy for hosts where ``predicate(host)``
is truthy. Hosts for which ``predicate(host)`` is falsey will be considered
:attr:`.IGNORED`, and will not be used in a query plan.
A :class:`.LoadBalancingPolicy` subclass configured with a child policy,
and a single-argument predicate. This policy defers to the child policy for
hosts where ``predicate(host)`` is truthy. Hosts for which
``predicate(host)`` is falsey will be considered :attr:`.IGNORED`, and will
not be used in a query plan.
This can be used in the cases where you need a whitelist or blacklist
policy, e.g. to prepare for decommissioning nodes or for testing:
@@ -494,6 +494,13 @@ class HostFilterPolicy(LoadBalancingPolicy):
_predicate = None
def __init__(self, child_policy, predicate):
"""
:param child_policy: an instantiated :class:`.LoadBalancingPolicy`
that this one will defer to.
:param predicate: a one-parameter function that takes a :class:`.Host`.
If it returns a falsey value, the :class:`.Host` will
be :attr:`.IGNORED` and not returned in query plans.
"""
super(HostFilterPolicy, self).__init__()
self._child_policy = child_policy
self._predicate = predicate