There is a way to do it slightly faster than in Yaroslav's answer by using get_operations. Here is a quick example:
import tensorflow as tf
a = tf.constant(1.3, name='const_a')
b = tf.Variable(3.1, name='variable_b')
c = tf.add(a, b, name='addition')
d = tf.multiply(c, a, name='multiply')
for op in tf.get_default_graph().get_operations():
print(str(op.name))