Python列表切片中的None

None起到增加维度的作用

def calc_mask_score(self, attention_mask):
        '''
        input: [b,n]
        output: [b,h,n,n]
        '''
        mask_score = torch.zeros(attention_mask.size(0),self.nums_heads,attention_mask.size(1),attention_mask.size(1)) # [b,h,n,n]
        mask_score = mask_score + attention_mask[:,None,None,:] # [b,n] => [b,h,n,n]
        mask_score = (1.0 - mask_score) * -10000.
        return mask_score