import tensorflow as tf
# declare two symbolic floating-point scalars
a = tf.placeholder(tf.float32)
b = tf.placeholder(tf.float32)
# create a simple symbolic expression using the add function
add = tf.add(a, b)
# bind 1.5 to  a  , 2.5 to  b  , and evaluate  c 
sess = tf.Session()
binding = {a: 1.5, b: 2.5}
c = sess.run(add, feed_dict=binding)
print(c)