SPPF.py

class SPPF(nn.Module):
    def __init__(self, in_channels, out_channels):
        super(SPPF, self).__init__()

        c_ = int(in_channels//2)

        self.c1 = CBL(in_channels, c_, 1, 1, 0)
        self.pool = nn.MaxPool2d(kernel_size=5, stride=1, padding=2)
        self.c_out = CBL(c_ * 4, out_channels, 1, 1, 0)

    def forward(self, x):
        x = self.c1(x)
        pool1 = self.pool(x)
        pool2 = self.pool(pool1)
        pool3 = self.pool(pool2)

        return self.c_out(torch.cat([x, pool1, pool2, pool3], dim=1))