Prints the names and counts of all elements present in an
    `etree._ElementTree`, e.g. a SaltDocument::

        SStructure: 65
        SSpan: 32
        SToken: 154
        STextualDS: 1

    Parameters
    ----------
    tree : lxml.etree._ElementTree
        an ElementTree that represents a complete SaltXML document
    element_type : str
        an XML tag, e.g. 'nodes', 'edges', 'labels'

def element_statistics(tree, element_type):
    """
    Prints the names and counts of all elements present in an
    `etree._ElementTree`, e.g. a SaltDocument::

        SStructure: 65
        SSpan: 32
        SToken: 154
        STextualDS: 1

    Parameters
    ----------
    tree : lxml.etree._ElementTree
        an ElementTree that represents a complete SaltXML document
    element_type : str
        an XML tag, e.g. 'nodes', 'edges', 'labels'
    """
    elements = get_elements(tree, element_type)
    stats = defaultdict(int)
    for i, element in enumerate(elements):
        stats[get_xsi_type(element)] += 1
    for (etype, count) in stats.items():
        print "{0}: {1}".format(etype, count)