'Class constructor.
Args:
optimizer_mapping (dict): dictionary specifying the mapping of layers to optimizers.
Key: ``\'default\'``, layer class name or layer `name` attribute.
Don\'t name your layers ``\'default\'``. Value: the optimizer object to
use for those layers.'

def __init__(self, optimizer_mapping, name=None):

    super(MultiOptimizer, self).__init__(name=name)
    self.optimizer_mapping = optimizer_mapping
    assert ('default' in self.optimizer_mapping), 'Must    specify    a    defaultoptimizer    in    layer    type    to    optimizer    mapping'
    self.map_list = None
    self.map_list_cache = dict()
