Specifically:

• seek() should actually perform a seek (this is not the case right now)
• allow callers to check if the iterator is currently valid (LevelDB::Iterator::Valid())
• allow callers to manually step the iterator forward and backward
• allow callers to fetch the key or value for a current iterator

This is a completely different model of iteration from standard python. As mentioned here:

tommetge@25364fc

... we have an existing code base whose logic depends on the outlined features. It may not be appropriate for the general Plyvel consumer.

Let me know what you think.