def deduplicate(sequence):
    """
    Return a list with all items of the input sequence but duplicates removed.

    Leaves the input sequence unaltered.
    """
    return [element
            for index, element in enumerate(sequence)
            if element not in sequence[:index]]

    Return a list with all items of the input sequence but duplicates removed.

    Leaves the input sequence unaltered.
    
watson/utils.py