The module Missing has interesting cmp behavior:

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import Missing b=[5,Missing.Value,0,-3,'c',Missing.Value,0,4,'a',Missing.Value, 'b',Missing.Value,6] b.sort() b [-3, 5, Missing.Value, 0, Missing.Value, 0, 4, Missing.Value, \ Missing.Value, 6, 'a', 'b', 'c']

As you can see, inserting a Missing.Value in the midst of a list, (particularly when juxtaposed with a zero) causes problems with numeric compares. Question: How should Missing.Values be sorted? Regardless of what their 'value' should be, I don't think they should disturb how other values are sorted. I'd recommend that they evaluate to less than all other values... Comments?