module_spec.py

# Copyright 2018 The TensorFlow Hub Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""ModuleSpec interface."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import abc


class ModuleSpec(object):
  """Represents the contents of a Module before it has been instantiated.

  A ModuleSpec is the blueprint used by `Module` to create one or more instances
  of a specific module in one or more graphs. The details on how to construct
  the Module are internal to the library implementation but methods to inspect
  a Module interface are public.

  Note: Do not instantiate this class directly. Use `hub.load_module_spec` or
  `hub.create_module_spec`.
  """
  __metaclass__ = abc.ABCMeta

  def __init__(self):
    """Do not instantiate directly."""
    pass

  @abc.abstractmethod
  def get_signature_names(self, tags=None):
    """Returns the module's signature names as an iterable of strings."""
    pass

  @abc.abstractmethod
  def get_tags(self):
    """Lists the graph variants as an iterable of set of tags."""
    return [set()]

  @abc.abstractmethod
  def get_input_info_dict(self, signature=None, tags=None):
    """Describes the inputs required by a signature.

    Args:
      signature: A string with the signature to get inputs information for.
        If None, the default signature is used if defined.
      tags: Optional set of strings, specifying the graph variant to query.

    Returns:
      A dict from input names to objects that provide (1) a property `dtype`,
      (2) a method `get_shape()` and (3) a read-only boolean property
      `is_sparse`. The first two are compatible with the common API of Tensor
      and SparseTensor objects.

    Raises:
      KeyError: if there is no such signature or graph variant.
    """
    raise NotImplementedError()

  @abc.abstractmethod
  def get_output_info_dict(self, signature=None, tags=None):
    """Describes the outputs provided by a signature.

    Args:
      signature: A string with the signature to get ouputs information for.
        If None, the default signature is used if defined.
      tags: Optional set of strings, specifying the graph variant to query.

    Returns:
      A dict from input names to objects that provide (1) a property `dtype`,
      (2) a method `get_shape()` and (3) a read-only boolean property
      `is_sparse`. The first two are compatible with the common API of Tensor
      and SparseTensor objects.

    Raises:
      KeyError: if there is no such signature or graph variant.
    """
    raise NotImplementedError()

  def get_attached_message(self, key, message_type, tags=None, required=False):
    """Returns the message attached to the module under the given key, or None.

    Module publishers can attach protocol messages to modules at creation time
    to provide module consumers with additional information, e.g., on module
    usage or provenance (see see hub.attach_message()). A typical use would be
    to store a small set of named values with modules of a certain type so
    that a support library for consumers of such modules can be parametric
    in those values.

    This method can also be called on a Module instantiated from a ModuleSpec,
    then `tags` are set to those used in module instatiation.

    Args:
      key: A string with the key of an attached message.
      message_type: A concrete protocol message class (*not* object) used
        to parse the attached message from its serialized representation.
        The message type for a particular key must be advertised with the key.
      tags: Optional set of strings, specifying the graph variant from which
        to read the attached message.
      required: An optional boolean. Setting it true changes the effect of
        an unknown `key` from returning None to raising a KeyError with text
        about attached messages.

    Returns:
      An instance of `message_type` with the message contents attached to the
      module, or `None` if `key` is unknown and `required` is False.

    Raises:
      KeyError: if `key` is unknown and `required` is True.
    """
    attached_bytes = self._get_attached_bytes(key, tags)
    if attached_bytes is None:
      if required:
        raise KeyError("No attached message for key '%s' in graph version %s "
                       "of Hub Module" % (key, sorted(tags or [])))
      else:
        return None
    message = message_type()
    message.ParseFromString(attached_bytes)
    return message

  @abc.abstractmethod
  def _get_attached_bytes(self, key, tags):
    """Internal implementation of the storage of attached messages.

    Args:
      key: The `key` argument to get_attached_message().
      tags: The `tags` argument to get_attached_message().

    Returns:
      The serialized message attached under `key` to the graph version
      identified by `tags`, or None if absent.
    """
    raise NotImplementedError()

  @abc.abstractmethod
  def _create_impl(self, name, trainable, tags):
    """Internal.

    Args:
      name: A string with the an unused name scope.
      trainable: A boolean, whether the Module is to be instantiated as
        trainable.
      tags: A set of strings specifying the graph variant to use.

    Returns:
      A ModuleImpl.
    """
    raise NotImplementedError()