tf.saved_model.save

Exports a tf.Module (and subclasses) obj to SavedModel format.

tf.saved_model.save(
    obj, export_dir, signatures=None, options=None
)

The obj must inherit from the Trackable class.

Example usage:

class Adder(tf.Module):
  @tf.function(input_signature=[tf.TensorSpec(shape=[], dtype=tf.float32)])
  def add(self, x):
    return x + x
 
model = Adder()
tf.saved_model.save(model, '/tmp/adder')

The resulting SavedModel is then servable with an input named "x", a scalar with dtype float32.

Signatures

Signatures define the input and output types for a computation. The optional save signatures argument controls which methods in obj will be available to programs which consume SavedModels, for example, serving APIs. Python functions may be decorated with @tf.function(input_signature=...) and passed as signatures directly, or lazily with a call to get_concrete_function on the method decorated with @tf.function.

Example:

class Adder(tf.Module):
  @tf.function
  def add(self, x):
    return x + x
 
model = Adder()
tf.saved_model.save(
  model, '/tmp/adder',signatures=model.add.get_concrete_function(
    tf.TensorSpec([], tf.float32)))

If a @tf.function does not have an input signature and get_concrete_function is not called on that method, the function will not be directly callable in the restored SavedModel.

Example:

class Adder(tf.Module):
  @tf.function
  def add(self, x):
    return x + x
 
model = Adder()
tf.saved_model.save(model, '/tmp/adder')
restored = tf.saved_model.load('/tmp/adder')
restored.add(1.)
Traceback (most recent call last):

ValueError: Found zero restored functions for caller function.

If the signatures argument is omitted, obj will be searched for @tf.function-decorated methods. If exactly one traced @tf.function is found, that method will be used as the default signature for the SavedModel. Else, any @tf.function attached to obj or its dependencies will be exported for use with tf.saved_model.load.

When invoking a signature in an exported SavedModel, Tensor arguments are identified by name. These names will come from the Python function's argument names by default. They may be overridden by specifying a name=... argument in the corresponding tf.TensorSpec object. Explicit naming is required if multiple Tensors are passed through a single argument to the Python function.

The outputs of functions used as signatures must either be flat lists, in which case outputs will be numbered, or a dictionary mapping string keys to Tensor, in which case the keys will be used to name outputs.

Signatures are available in objects returned by tf.saved_model.load as a .signatures attribute. This is a reserved attribute: tf.saved_model.save on an object with a custom .signatures attribute will raise an exception.

_Using tf.savedmodel.save with Keras models

While Keras has its own saving and loading API, this function can be used to export Keras models. For example, exporting with a signature specified:

class Adder(tf.keras.Model):
  @tf.function(input_signature=[tf.TensorSpec(shape=[], dtype=tf.string)])
  def concat(self, x):
     return x + x
 
model = Adder()
tf.saved_model.save(model, '/tmp/adder')

Exporting from a function without a fixed signature:

class Adder(tf.keras.Model):
  @tf.function
  def concat(self, x):
     return x + x
 
model = Adder()
tf.saved_model.save(
  model, '/tmp/adder',
  signatures=model.concat.get_concrete_function(
    tf.TensorSpec(shape=[], dtype=tf.string, name="string_input")))

tf.keras.Model instances constructed from inputs and outputs already have a signature and so do not require a @tf.function decorator or a signatures argument. If neither are specified, the model's forward pass is exported.

x = tf.keras.layers.Input((4,), name="x")
y = tf.keras.layers.Dense(5, name="out")(x)
model = tf.keras.Model(x, y)
tf.saved_model.save(model, '/tmp/saved_model/')

The exported SavedModel takes "x" with shape [None, 4] and returns "out" with shape [None, 5]

Variables and Checkpoints

Variables must be tracked by assigning them to an attribute of a tracked object or to an attribute of obj directly. TensorFlow objects (e.g. layers from tf.keras.layers, optimizers from tf.train) track their variables automatically. This is the same tracking scheme that tf.train.Checkpoint uses, and an exported Checkpoint object may be restored as a training checkpoint by pointing tf.train.Checkpoint.restore to the SavedModel's "variables/" subdirectory.

tf.function does not hard-code device annotations from outside the function body, instead of using the calling context's device. This means for example that exporting a model that runs on a GPU and serving it on a CPU will generally work, with some exceptions:

  • tf.device annotations inside the body of the function will be hard-coded in the exported model; this type of annotation is discouraged.
  • Device-specific operations, e.g. with "cuDNN" in the name or with device-specific layouts, may cause issues.
  • For ConcreteFunctions, active distribution strategies will cause device placements to be hard-coded in the function.

SavedModels exported with tf.saved_model.save strip default-valued attributes automatically, which removes one source of incompatibilities when the consumer of a SavedModel is running an older TensorFlow version than the producer. There are however other sources of incompatibilities which are not handled automatically, such as when the exported model contains operations which the consumer does not have definitions for.

obj A trackable object (e.g. tf.Module or tf.train.Checkpoint) to export.
export_dir A directory in which to write the SavedModel.
signatures Optional, one of three types:

  • a tf.function with an input signature specified, which will use the default serving signature key,
  • the result of f.get_concrete_function on a @tf.function-decorated function f, in which case f will be used to generate a signature for the SavedModel under the default serving signature key,
  • a dictionary, which maps signature keys to either tf.function instances with input signatures or concrete functions. Keys of such a dictionary may be arbitrary strings, but will typically be from the tf.saved_model.signature_constants module.
options tf.saved_model.SaveOptions object for configuring save options.

ValueError If obj is not trackable.

Eager Compatibility

Not well supported when graph building. From TensorFlow 1.x, tf.compat.v1.enable_eager_execution() should run first. Calling tf.saved_model.save in a loop when graph building from TensorFlow 1.x will add new save operations to the default graph each iteration.

May not be called from within a function body.