# Codeblock 7a
class Bottleneck(nn.Module):
    def __init__(self, 
                 in_channels, 
                 out_channels, 
                 kernel_size, 
                 stride,
                 padding,
                 exp_size,     #(1)
                 se,           #(2)
                 activation):
        super().__init__()

        self.add = in_channels == out_channels and stride == 1    #(3)

        self.conv0 = ConvBlock(in_channels=in_channels,    #(4)
                               out_channels=exp_size,    #(5)
                               kernel_size=1,    #(6)
                               stride=1, 
                               padding=0,
                               activation=activation)
                               
        self.conv1 = ConvBlock(in_channels=exp_size,    #(7)
                               out_channels=exp_size,    #(8)
                               kernel_size=kernel_size,    #(9)
                               stride=stride, 
                               padding=padding,
                               groups=exp_size,    #(10)
                               activation=activation)

        self.semodule = SEModule(num_channels=exp_size, r=4) if se else nn.Identity()    #(11)

        self.conv2 = ConvBlock(in_channels=exp_size,    #(12)
                               out_channels=out_channels,    #(13)
                               kernel_size=1,    #(14)
                               stride=1, 
                               padding=0, 
                               activation=nn.Identity())    #(15)