'A list of placement groups.
:param names: Placement Group names
:type names: ``list`` of ``str``
:rtype: ``list`` of :class:`.EC2PlacementGroup`'

def ex_list_placement_groups(self, names=None):

    names = (names or [])
    params = {'Action': 'DescribePlacementGroups'}
    for (index, name) in enumerate(names):
        params[(('GroupName.%s' % index) + 1)] = name
    response = self.connection.request(self.path, params=params).object
    return self._to_placement_groups(response)
