TensorFlow如何解析函数

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""解析相关的帮助函数在`input_fn`中使用.""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import six

from tensorflow.python.feature_column import feature_column as fc
from tensorflow.python.framework import dtypes
from tensorflow.python.ops import parsing_ops


def classifier_parse_example_spec(feature_columns,
                                  label_key,
                                  label_dtype=dtypes.int64,
                                  label_default=None,
                                  weight_column=None):
  """Generates parsing spec for tf.parse_example to be used with classifiers.
  If users keep data in tf.Example format, they need to call tf.parse_example
  with a proper feature spec. There are two main things that this utility helps:
  * Users need to combine parsing spec of features with labels and weights
    (if any) since they are all parsed from same tf.Example instance. This
    utility combines these specs.
  * It is difficult to map expected label by a classifier such as
    `DNNClassifier` to corresponding tf.parse_example spec. This utility encodes
    it by getting related information from users (key, dtype).
  Example output of parsing spec:
  ```python
  # Define features and transformations
  feature_b = tf.feature_column.numeric_column(...)
  feature_c_bucketized = tf.feature_column.bucketized_column(
    tf.feature_column.numeric_column("feature_c"), ...)
  feature_a_x_feature_c = tf.feature_column.crossed_column(
      columns=["feature_a", feature_c_bucketized], ...)
  feature_columns = [feature_b, feature_c_bucketized, feature_a_x_feature_c]
  parsing_spec = tf.estimator.classifier_parse_example_spec(
      feature_columns, label_key='my-label', label_dtype=tf.string)
  # For the above example, classifier_parse_example_spec would return the dict:
  assert parsing_spec == {
    "feature_a": parsing_ops.VarLenFeature(tf.string),
    "feature_b": parsing_ops.FixedLenFeature([1], dtype=tf.float32),
    "feature_c": parsing_ops.FixedLenFeature([1], dtype=tf.float32)
    "my-label" : parsing_ops.FixedLenFeature([1], dtype=tf.string)
  }
  ```
  Example usage with a classifier:
  ```python
  feature_columns = # define features via tf.feature_column
  estimator = DNNClassifier(
      n_classes=1000,
      feature_columns=feature_columns,
      weight_column='example-weight',
      label_vocabulary=['photos', 'keep', ...],
      hidden_units=[256, 64, 16])
  # This label configuration tells the classifier the following:
  # * weights are retrieved with key 'example-weight'
  # * label is string and can be one of the following ['photos', 'keep', ...]
  # * integer id for label 'photos' is 0, 'keep' is 1, ...
  # Input builders
  def input_fn_train():  # Returns a tuple of features and labels.
    features = tf.contrib.learn.read_keyed_batch_features(
        file_pattern=train_files,
        batch_size=batch_size,
        # creates parsing configuration for tf.parse_example
        features=tf.estimator.classifier_parse_example_spec(
            feature_columns,
            label_key='my-label',
            label_dtype=tf.string,
            weight_column='example-weight'),
        reader=tf.RecordIOReader)
     labels = features.pop('my-label')
     return features, labels
  estimator.train(input_fn=input_fn_train)
  ```
  Args:
    feature_columns: An iterable containing all feature columns. All items
      should be instances of classes derived from `_FeatureColumn`.
    label_key: A string identifying the label. It means tf.Example stores labels
      with this key.
    label_dtype: A `tf.dtype` identifies the type of labels. By default it is
      `tf.int64`. If user defines a `label_vocabulary`, this should be set as
      `tf.string`. `tf.float32` labels are only supported for binary
      classification.
    label_default: used as label if label_key does not exist in given
      tf.Example. An example usage: let's say `label_key` is 'clicked' and
      tf.Example contains clicked data only for positive examples in following
      format `key:clicked, value:1`. This means that if there is no data with
      key 'clicked' it should count as negative example by setting
      `label_deafault=0`. Type of this value should be compatible with
      `label_dtype`.
    weight_column: A string or a `_NumericColumn` created by
      `tf.feature_column.numeric_column` defining feature column representing
      weights. It is used to down weight or boost examples during training. It
      will be multiplied by the loss of the example. If it is a string, it is
      used as a key to fetch weight tensor from the `features`. If it is a
      `_NumericColumn`, raw tensor is fetched by key `weight_column.key`,
      then weight_column.normalizer_fn is applied on it to get weight tensor.
  Returns:
    A dict mapping each feature key to a `FixedLenFeature` or `VarLenFeature`
    value.
  Raises:
    ValueError: If label is used in `feature_columns`.
    ValueError: If weight_column is used in `feature_columns`.
    ValueError: If any of the given `feature_columns` is not a `_FeatureColumn`
      instance.
    ValueError: If `weight_column` is not a `_NumericColumn` instance.
    ValueError: if label_key is None.
  """
  parsing_spec = fc.make_parse_example_spec(feature_columns)
  if label_key in parsing_spec:
    raise ValueError('label should not be used as feature. '
                     'label_key: {}, features: {}'.format(
                         label_key, parsing_spec.keys()))
  parsing_spec[label_key] = parsing_ops.FixedLenFeature((1,), label_dtype,
                                                        label_default)

  if weight_column is None:
    return parsing_spec

  if isinstance(weight_column, six.string_types):
    weight_column = fc.numeric_column(weight_column)

  if not isinstance(weight_column, fc._NumericColumn):  # pylint: disable=protected-access
    raise ValueError('weight_column should be an instance of '
                     'tf.feature_column.numeric_column. '
                     'Given type: {} value: {}'.format(
                         type(weight_column), weight_column))

  if weight_column.key in parsing_spec:
    raise ValueError('weight_column should not be used as feature. '
                     'weight_column: {}, features: {}'.format(
                         weight_column.key, parsing_spec.keys()))

  parsing_spec.update(weight_column._parse_example_spec)  # pylint: disable=protected-access
  return parsing_spec


def regressor_parse_example_spec(feature_columns,
                                 label_key,
                                 label_dtype=dtypes.float32,
                                 label_default=None,
                                 label_dimension=1,
                                 weight_column=None):
  """Generates parsing spec for tf.parse_example to be used with regressors.
  If users keep data in tf.Example format, they need to call tf.parse_example
  with a proper feature spec. There are two main things that this utility helps:
  * Users need to combine parsing spec of features with labels and weights
    (if any) since they are all parsed from same tf.Example instance. This
    utility combines these specs.
  * It is difficult to map expected label by a regressor such as `DNNRegressor`
    to corresponding tf.parse_example spec. This utility encodes it by getting
    related information from users (key, dtype).
  Example output of parsing spec:
  ```python
  # Define features and transformations
  feature_b = tf.feature_column.numeric_column(...)
  feature_c_bucketized = tf.feature_column.bucketized_column(
    tf.feature_column.numeric_column("feature_c"), ...)
  feature_a_x_feature_c = tf.feature_column.crossed_column(
      columns=["feature_a", feature_c_bucketized], ...)
  feature_columns = [feature_b, feature_c_bucketized, feature_a_x_feature_c]
  parsing_spec = tf.estimator.regressor_parse_example_spec(
      feature_columns, label_key='my-label')
  # For the above example, regressor_parse_example_spec would return the dict:
  assert parsing_spec == {
    "feature_a": parsing_ops.VarLenFeature(tf.string),
    "feature_b": parsing_ops.FixedLenFeature([1], dtype=tf.float32),
    "feature_c": parsing_ops.FixedLenFeature([1], dtype=tf.float32)
    "my-label" : parsing_ops.FixedLenFeature([1], dtype=tf.float32)
  }
  ```
  Example usage with a regressor:
  ```python
  feature_columns = # define features via tf.feature_column
  estimator = DNNRegressor(
      hidden_units=[256, 64, 16],
      feature_columns=feature_columns,
      weight_column='example-weight',
      label_dimension=3)
  # This label configuration tells the regressor the following:
  # * weights are retrieved with key 'example-weight'
  # * label is a 3 dimension tensor with float32 dtype.
  # Input builders
  def input_fn_train():  # Returns a tuple of features and labels.
    features = tf.contrib.learn.read_keyed_batch_features(
        file_pattern=train_files,
        batch_size=batch_size,
        # creates parsing configuration for tf.parse_example
        features=tf.estimator.classifier_parse_example_spec(
            feature_columns,
            label_key='my-label',
            label_dimension=3,
            weight_column='example-weight'),
        reader=tf.RecordIOReader)
     labels = features.pop('my-label')
     return features, labels
  estimator.train(input_fn=input_fn_train)
  ```
  Args:
    feature_columns: An iterable containing all feature columns. All items
      should be instances of classes derived from `_FeatureColumn`.
    label_key: A string identifying the label. It means tf.Example stores labels
      with this key.
    label_dtype: A `tf.dtype` identifies the type of labels. By default it is
      `tf.float32`.
    label_default: used as label if label_key does not exist in given
      tf.Example. By default default_value is none, which means
      `tf.parse_example` will error out if there is any missing label.
    label_dimension: Number of regression targets per example. This is the
      size of the last dimension of the labels and logits `Tensor` objects
      (typically, these have shape `[batch_size, label_dimension]`).
    weight_column: A string or a `_NumericColumn` created by
      `tf.feature_column.numeric_column` defining feature column representing
      weights. It is used to down weight or boost examples during training. It
      will be multiplied by the loss of the example. If it is a string, it is
      used as a key to fetch weight tensor from the `features`. If it is a
      `_NumericColumn`, raw tensor is fetched by key `weight_column.key`,
      then weight_column.normalizer_fn is applied on it to get weight tensor.
  Returns:
    A dict mapping each feature key to a `FixedLenFeature` or `VarLenFeature`
    value.
  Raises:
    ValueError: If label is used in `feature_columns`.
    ValueError: If weight_column is used in `feature_columns`.
    ValueError: If any of the given `feature_columns` is not a `_FeatureColumn`
      instance.
    ValueError: If `weight_column` is not a `_NumericColumn` instance.
    ValueError: if label_key is None.
  """
  parsing_spec = fc.make_parse_example_spec(feature_columns)
  if label_key in parsing_spec:
    raise ValueError('label should not be used as feature. '
                     'label_key: {}, features: {}'.format(
                         label_key, parsing_spec.keys()))
  parsing_spec[label_key] = parsing_ops.FixedLenFeature(
      (label_dimension,), label_dtype, label_default)

  if weight_column is None:
    return parsing_spec

  if isinstance(weight_column, six.string_types):
    weight_column = fc.numeric_column(weight_column)

  if not isinstance(weight_column, fc._NumericColumn):  # pylint: disable=protected-access
    raise ValueError('weight_column should be an instance of '
                     'tf.feature_column.numeric_column. '
                     'Given type: {} value: {}'.format(
                         type(weight_column), weight_column))

  if weight_column.key in parsing_spec:
    raise ValueError('weight_column should not be used as feature. '
                     'weight_column: {}, features: {}'.format(
                         weight_column.key, parsing_spec.keys()))

  parsing_spec.update(weight_column._parse_example_spec)  # pylint: disable=protected-access
  return parsing_spec