tensorflow报错： Cannot evaluate tensor using `eval()`

import tensorflow as tf

#两层简单神经网络

x = tf.placeholder(tf.float32, shape=(1,2))
w1 = tf.Variable(tf.random_normal([2,3], stddev=1, seed=1))
w2 = tf.Variable(tf.random_normal([3,1], stddev=1, seed=1))

#定义前向传播过程
a = tf.matmul(x,w1)
y = tf.matmul(a,w2)

#使用会话计算结果
with tf.Session() as sess:
    init_op = tf.global_variables_initializer()
    sess.run(init_op)
    print(sess.run(y, feed_dict={x:[[0.7,0.5]]}))

TensorFlow版本为2.6.0

报错结果：

 File "C:/Users/ThinkPad/PycharmProjects/tensorflowtest1/main.py", line 84, in <module>
    one.eval()
  File "C:\Users\ThinkPad\PycharmProjects\tensorflowtest1\venv\lib\site-packages\tensorflow\python\framework\ops.py", line 936, in eval
    return _eval_using_default_session(self, feed_dict, self.graph, session)
  File "C:\Users\ThinkPad\PycharmProjects\tensorflowtest1\venv\lib\site-packages\tensorflow\python\framework\ops.py", line 5533, in _eval_using_default_session
    raise ValueError("Cannot evaluate tensor using `eval()`: No default "
ValueError: Cannot evaluate tensor using `eval()`: No default session is registered. Use `with sess.as_default()` or pass an explicit session to `eval(session=sess)`