def partition_asymmetry(bif_point):
assert len(bif_point.children) == <NUM_LIT:2>, '<STR_LIT>'<EOL>n = float(sum(<NUM_LIT:1> for _ in bif_point.children[<NUM_LIT:0>].ipreorder()))<EOL>m = float(sum(<NUM_LIT:1> for _ in bif_point.children[<NUM_LIT:1>].ipreorder()))<EOL>if n == m:<EOL><INDENT>return <NUM_LIT:0.0><EOL><DEDENT>return abs(n - m) / abs(n + m)<EOL>
Calculate the partition asymmetry at a bifurcation point
    as defined in https://www.ncbi.nlm.nih.gov/pubmed/18568015

    The number of nodes in each child tree is counted. The partition
    is defined as the ratio of the absolute difference and the sum
    of the number of bifurcations in the two daughter subtrees
    at each branch point.