This is why I prefer the API exposed by https://pypi.org/project/toposort/

list(toposort({2: {11},
               9: {11, 8, 10},
               10: {11, 3},
               11: {7, 5},
               8: {7, 3},
              }))

returns [{3, 5, 7}, {8, 11}, {2, 10}, {9}]

For an node with no edges, use an empty set:

list(toposort({100: set(),
               2: {11},
               9: {11, 8, 10},
               10: {11, 3},
               11: {7, 5},
               8: {7, 3},
              }))
[{3, 100, 5, 7}, {8, 11}, {2, 10}, {9}]

I also don't think we should provide multiple APIs. Let's just provide one, and recipes for any helpers, if needed. For example, to flatten the result into a list. Or to take a list of edges as the input.