def unique( it ):
    """unique( it ) => iterator

    Generate each value from the input iterator "it" exactly once
    ordered according to the first occurance of the value.
    """
    seen = set()
    for v in it:
        if v in seen: continue
        seen.add( v )
        yield v
unique( it ) => iterator

    Generate each value from the input iterator "it" exactly once
    ordered according to the first occurance of the value.
    
recipes/Python/577473_Named_Sequences_environments_containing_large/recipe-577473.py