Yes, the callable could create only a few non-zero entries. And only the
non-zero entries are retained in the SparseMatrix so it is reasonable to
keep that code:
>>> SparseMatrix(3,3,lambda i,j: 1 if i==j else 0)
[1, 0, 0]
[0, 1, 0]
[0, 0, 1]
>>> _._smat
{(0, 0): 1, (1, 1): 1, (2, 2): 1}
Again, the "else" part allows dense input that has few entries to be stored
in a compact way so there's no reason to disallow it AFAICT:
>>> SparseMatrix([[0,0,1],[0,0,1]])
[0, 0, 1]
[0, 0, 1]
>>> _._smat
{(1, 2): 1, (0, 2): 1}
>>> SparseMatrix(3,3,lambda i,j: 1 if i==j else 0)
(The bugginess that Aaron refers to is perhaps refering to the former state
of SparseMatrix; I think things are currently in pretty good shape.)
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