Function walked_source 

pub fn walked_source(
    tables: &[Steps],
    shape: &[usize],
    len: usize,
) -> Option<Vec<usize>>

The row-major shape of a source of len items whose axes the entries of tables step along, for a copy of shape, for a caller that holds a source’s storage without its shape, as a Python view does. It has one axis for each distinct stride, and each axis holds as many items as the next larger stride spans. None where a stride doesn’t divide the next, or len isn’t a whole number of the largest.