Purpose of '*' in front of Python3 function

Question

I saw the code for a ResNet CNN in Python3 and PyTorch here as follows:

def resnet_block(input_channels, num_channels, num_residuals,
                 first_block=False):
    blk = []
    for i in range(num_residuals):
        if i == 0 and not first_block:
            blk.append(Residual(input_channels, num_channels,
                                use_1x1conv=True, strides=2))
        else:
            blk.append(Residual(num_channels, num_channels))
    return blk

To add the modules, the following code is used-

b2 = nn.Sequential(*resnet_block(64, 64, 2, first_block=True))
b3 = nn.Sequential(*resnet_block(64, 128, 2))
b4 = nn.Sequential(*resnet_block(128, 256, 2))
b5 = nn.Sequential(*resnet_block(256, 512, 2))

What does "*resnet_block()" mean/do?

Answer 1

Basically *iterable is used to unpack the items of an iterable object as positional arguments. In your question resnet_block returns a list, and the items of that list are passed to nn.Sequential rather than the list itself.