def lengths_to_padding_mask(lengths: Tensor) -> Tensor:
    """Convert lengths of shape (B, ) to padding mask."""
    batch_size = lengths.shape[0]
    max_length = int(torch.max(lengths).item())
    padding_mask = torch.arange(  # [0, ..., T-1]
        max_length, device=lengths.device, dtype=lengths.dtype
    ).expand(batch_size, max_length) >= lengths.unsqueeze(1)

    return padding_mask
Convert lengths of shape (B, ) to padding mask.
fairseq/models/speech_to_text/utils.py