Either a checkpoint prefix or the name of a directory to save the
checkpoint in (in which case the checkpoint will be named based on the
Network name).
global_step
The global step to use when naming the checkpoint. If None
(default), we will first try to get the default global step. If that fails
because no default global step exists, then the checkpoint is created
without a global step suffix.
map_func
A function mapping fully qualified variable names (e.g.
'my_network_1/dense_1/kernel') to names in the checkpoint. By default (if
map_func=None), the variable prefix for the network being restored
(Network.scope_name + '/', e.g. 'my_network_1/') is stripped and all
other variable names (shared with other Networks) are left unchanged.
Returns
The checkpoint prefix for the saved checkpoint, which may be passed to
Network.restore.
Raises
ValueError
If the Network has not yet been called, or if map_func results
in a name collision.