python 变量@变量

出现在一行代码中间位置的@这个@是矩阵相乘的意思，

就是比如
A的shape是[batch_size, sequence_length2, sequence_length1]
B的shape是[batch_size, sequence_length1, hidden_dim]
C = A @ B
则C的shape是[batch_size, sequence_length2, hidden_dim]