'Convert this matrix into Block Sparse Row Format.
With copy=False, the data/indices may be shared between this
matrix and the resultant bsr_matrix.
If blocksize=(R, C) is provided, it will be used for determining
block size of the bsr_matrix.'

def tobsr(self, blocksize=None, copy=False):

    if (blocksize not in [None, self.blocksize]):
        return self.tocsr().tobsr(blocksize=blocksize)
    if copy:
        return self.copy()
    else:
        return self
