This is because most of the current DGL APIs already support multigraph cases and we feel it is not necessary for users to specify that anymore. For example, the
g.in_degrees API can correctly count the parallel edges and the
g.update_all API will aggregate messages from those edges too.
There are a few exceptions. For example,
g.edge_ids(u, v) returns the id for each edge pair. In a multigraph case, there could be multiple edge ids for the same
(u, v) pair. Therefore, you can specify
g.edge_ids(u, v, return_uv=True) to return
(u, v, eid) tuple of tensors to distinguish each
(u, v) pair. Since this kinds of APIs are rare, we just add flags for each of them making the
multigraph flag essentially redundant.