What are the colons after class names in Python? Do they define scope or namespaces?

Question

In the code I found here (listed below), there are lines like fid: torch.Tensor = piq.FID()(x_features, y_features) and kid: torch.Tensor = piq.KID()(x_features, y_features). What are the fid: and kid: ? I opened the code in Visual Studio, but there was no syntax highlight for it. Is such syntax part of standard Python or is it something specific to PyTorch? In Q-BASIC, such words ending with a colon were subroutine names. But here it seems to serve a different purpose. Even the print(f"FID: {fid:0.4f}") was surprising. Is this a way of specifying a namespace or something?

Any official Python page that explains such a syntax?

import torch
import piq


@torch.no_grad()
def main():
    x_features = torch.rand(2000, 128)
    y_features = torch.rand(2000, 128)

    if torch.cuda.is_available():
        # Move to GPU to make computaions faster
        x_features = x_features.cuda()
        y_features = y_features.cuda()

    # Use FID class to compute FID score from image features, pre-extracted from some feature extractor network
    fid: torch.Tensor = piq.FID()(x_features, y_features)
    print(f"FID: {fid:0.4f}")

    # If image features are not available, extract them using compute_feats of FID class.
    # Please note that compute_feats consumes a data loader of predefined format.

    # Use GS class to compute Geometry Score from image features, pre-extracted from some feature extractor network.
    # Computation is heavily CPU dependent, adjust num_workers parameter according to your system configuration.
    gs: torch.Tensor = piq.GS(sample_size=64, num_iters=100, i_max=100, num_workers=4)(x_features, y_features)
    print(f"GS: {gs:0.4f}")

    # Use inception_score function to compute IS from image features, pre-extracted from some feature extractor network.
    # Note, that we follow recommendations from paper "A Note on the Inception Score"
    isc_mean, _ = piq.inception_score(x_features, num_splits=10)
    # To compute difference between IS for 2 sets of image features, use IS class.
    isc: torch.Tensor = piq.IS(distance='l1')(x_features, y_features)
    print(f"IS: {isc_mean:0.4f}, difference: {isc:0.4f}")

    # Use KID class to compute KID score from image features, pre-extracted from some feature extractor network:
    kid: torch.Tensor = piq.KID()(x_features, y_features)
    print(f"KID: {kid:0.4f}")

    # Use MSID class to compute MSID score from image features, pre-extracted from some feature extractor network:
    msid: torch.Tensor = piq.MSID()(x_features, y_features)
    print(f"MSID: {msid:0.4f}")


if __name__ == '__main__':
    main()