Build a eval_input_receiver_fn expecting fed tf.Examples.

Creates a eval_input_receiver_fn that expects a serialized tf.Example fed into a string placeholder. The function parses the tf.Example according to the provided feature_spec, and returns all parsed Tensors as features.

feature_spec A dict of string to VarLenFeature/FixedLenFeature.
label_key The key for the label column in the feature_spec. Note that the label must be part of the feature_spec. If None, does not pass a label to the EvalInputReceiver (note that label_key must be None and not simply the empty string for this case).

A eval_input_receiver_fn suitable for use with TensorFlow model analysis.