To answer Mark, even though no longer nosy: In general, sequence methods .count, .index, and .__contains__ take sequence members and only members as arguments.  Unicode sequences are exceptional because codepoints are not Python objects, so string subsequences must be used instead.  Byte-like sequences are also exceptional in that both members and subsequences are accepted for these methods.

String-like sequence methods .split and .partition take subsequences as arguments.  I think the doc should make this clearer.