It seems that the documentation has a problem. For example, the most useful functions such as fit or evaluate in the documentation of tf.contrib.learn is as follows:

tf.contrib.learn.Estimator.fit(x=None, y=None, input_fn=None, steps=None, batch_size=None, monitors=None, max_steps=None)

See Trainable.

Raises:

ValueError: If x or y are not None while input_fn is not None.
ValueError: If both steps and max_steps are not None.

Trainable does not linked or described in the generated documentation. It's really annoying issue for beginners.