如何在tensorflow中列出图形中的变量？

import tensorflow as tf

# 创建一个图形
graph = tf.Graph()

# 在图形中定义一些变量
with graph.as_default():
    var1 = tf.Variable(1, name='var1')
    var2 = tf.Variable(2, name='var2')
    var3 = tf.Variable(3, name='var3')

# 列出图形中的变量
with tf.Session(graph=graph) as sess:
    sess.run(tf.global_variables_initializer())
    variables = tf.global_variables()
    for var in variables:
        print(var.name)

var1:0
var2:0
var3:0