def indentation_step(node):
    """
    Dirty little trick to get the difference between each indentation level
    Implemented by finding the shortest indentation string
    (technically, the "least" of all of the indentation strings, but
    tabs and spaces mixed won't get this far, so those are synonymous.)
    """
    r = find_root(node)
    # Collect all indentations into one set.
    all_indents = set(i.value for i in r.pre_order() if i.type == token.INDENT)
    if not all_indents:
        # nothing is indented anywhere, so we get to pick what we want
        return u"    " # four spaces is a popular convention
    else:
        return min(all_indents)