eval(feed_dict=None, session=None) method of tensorflow.python.framework.ops.Tensor instance
Evaluates（评价） this tensor in a `Session`.
Calling this method will execute（执行） all preceding operations that
produce the inputs needed for the operation that produces this
tensor.
*N.B.* Before invoking `Tensor.eval()`, its graph must have been
launched in a session, and either a default session must be
available, or `session` must be specified explicitly.
Args:
feed_dict: A dictionary that maps `Tensor` objects to feed values.
See @{tf.Session.run} for a
description of the valid feed values.
session: (Optional.) The `Session` to be used to evaluate this tensor. If
none, the default session will be used.
