def reduce_tree()

in Lib/lib2to3/btm_utils.py [0:0]

• 92 lines of code
• 47 McCabe index (conditional complexity)

def reduce_tree(node, parent=None):
    """
    Internal function. Reduces a compiled pattern tree to an
    intermediate representation suitable for feeding the
    automaton. This also trims off any optional pattern elements(like
    [a], a*).
    """

    new_node = None
    #switch on the node type
    if node.type == syms.Matcher:
        #skip
        node = node.children[0]

    if node.type == syms.Alternatives  :
        #2 cases
        if len(node.children) <= 2:
            #just a single 'Alternative', skip this node
            new_node = reduce_tree(node.children[0], parent)
        else:
            #real alternatives
            new_node = MinNode(type=TYPE_ALTERNATIVES)
            #skip odd children('|' tokens)
            for child in node.children:
                if node.children.index(child)%2:
                    continue
                reduced = reduce_tree(child, new_node)
                if reduced is not None:
                    new_node.children.append(reduced)
    elif node.type == syms.Alternative:
        if len(node.children) > 1:

            new_node = MinNode(type=TYPE_GROUP)
            for child in node.children:
                reduced = reduce_tree(child, new_node)
                if reduced:
                    new_node.children.append(reduced)
            if not new_node.children:
                # delete the group if all of the children were reduced to None
                new_node = None

        else:
            new_node = reduce_tree(node.children[0], parent)

    elif node.type == syms.Unit:
        if (isinstance(node.children[0], pytree.Leaf) and
            node.children[0].value == '('):
            #skip parentheses
            return reduce_tree(node.children[1], parent)
        if ((isinstance(node.children[0], pytree.Leaf) and
               node.children[0].value == '[')
               or
               (len(node.children)>1 and
               hasattr(node.children[1], "value") and
               node.children[1].value == '[')):
            #skip whole unit if its optional
            return None

        leaf = True
        details_node = None
        alternatives_node = None
        has_repeater = False
        repeater_node = None
        has_variable_name = False

        for child in node.children:
            if child.type == syms.Details:
                leaf = False
                details_node = child
            elif child.type == syms.Repeater:
                has_repeater = True
                repeater_node = child
            elif child.type == syms.Alternatives:
                alternatives_node = child
            if hasattr(child, 'value') and child.value == '=': # variable name
                has_variable_name = True

        #skip variable name
        if has_variable_name:
            #skip variable name, '='
            name_leaf = node.children[2]
            if hasattr(name_leaf, 'value') and name_leaf.value == '(':
                # skip parenthesis
                name_leaf = node.children[3]
        else:
            name_leaf = node.children[0]

        #set node type
        if name_leaf.type == token_labels.NAME:
            #(python) non-name or wildcard
            if name_leaf.value == 'any':
                new_node = MinNode(type=TYPE_ANY)
            else:
                if hasattr(token_labels, name_leaf.value):
                    new_node = MinNode(type=getattr(token_labels, name_leaf.value))
                else:
                    new_node = MinNode(type=getattr(pysyms, name_leaf.value))

        elif name_leaf.type == token_labels.STRING:
            #(python) name or character; remove the apostrophes from
            #the string value
            name = name_leaf.value.strip("'")
            if name in tokens:
                new_node = MinNode(type=tokens[name])
            else:
                new_node = MinNode(type=token_labels.NAME, name=name)
        elif name_leaf.type == syms.Alternatives:
            new_node = reduce_tree(alternatives_node, parent)

        #handle repeaters
        if has_repeater:
            if repeater_node.children[0].value == '*':
                #reduce to None
                new_node = None
            elif repeater_node.children[0].value == '+':
                #reduce to a single occurrence i.e. do nothing
                pass
            else:
                #TODO: handle {min, max} repeaters
                raise NotImplementedError
                pass

        #add children
        if details_node and new_node is not None:
            for child in details_node.children[1:-1]:
                #skip '<', '>' markers
                reduced = reduce_tree(child, new_node)
                if reduced is not None:
                    new_node.children.append(reduced)
    if new_node:
        new_node.parent = parent
    return new_node