C Template List GDB printer: V1 Python

import gdb

# generic utility to pretty-print a linked list
# it terminates on NULL pointer or if it detects a cycle
def linked_list_children_list(first_node, func_next_node, func_item_of_node = None):
    if not func_item_of_node:
        func_item_of_node = lambda p: p
    pnode = first_node
    visited_addresses = set()
    k = 0
    while pnode and int(pnode) != 0:
        name = '[%d]' % k
        cycled = int(pnode) in visited_addresses
        if cycled:
            name = '[cycle]'
        yield (name, func_item_of_node(pnode))
        k += 1
        visited_addresses.add(int(pnode))
        if cycled:
            break
        pnode = func_next_node(pnode)

#=========================================================================

class ListPrinter:
    # NOTE: static variable which stores user-specified value type
    value_type = None

    def __init__(self, value):
        self.value = value

    def to_string(self):
        return 'List[%d]' % int(self.value['count'])

    def print_node_value(self, value):
        if int(value) == 0:
            return value
        vtype = ListPrinter.value_type
        if vtype is None:
            return value
        # here we cast to the desired type
        return value.cast(vtype.pointer()).dereference()

    def children(self):
        # this is generic function for pretty-printing linked lists
        return linked_list_children_list(
            # start node
            self.value['head'].dereference()['next'],
            # given a node, returns the next node
            lambda x: x.dereference()['next'],
            # given a node, returns the value of the node
            lambda x: self.print_node_value(x.dereference()['data'])
        )

# unfortunately, GDB does not automatically match pointer type
# if value type is assigned to a pretty printer
# so if you want to inspect variables of type 'xlist *',
# you also have to make and register a pretty printer for pointer =(
class ListPtrPrinter:
    def __init__(self, value):
        self.value = value
        self.printer = ListPrinter(value)
    def to_string(self):
        return '0x%x ' % int(self.value) + self.printer.to_string()
    def children(self):
        return self.printer.children()

# I could not make RegexpCollectionPrettyPrinter match pointers
# so we have to use the worse approach for registration
def ppmatcher(value):
    if str(value.type) in ['xlist']:
        return ListPrinter(value)
    if str(value.type) in ['xlist *', 'List']:
        return ListPtrPrinter(value)
    return None

if ppmatcher in gdb.pretty_printers:
    del gdb.pretty_printers[gdb.pretty_printers.index(ppmatcher)]
gdb.pretty_printers.append(ppmatcher)


# user command that it directly runnable from the GDB console
class SetListType(gdb.Command):
    def __init__(self):
        super(SetListType, self).__init__('set_list_type', gdb.COMMAND_USER)

    def invoke(self, argument, fromtty):
        argv = gdb.string_to_argv(argument)
        if len(argv) != 1:
            print('Pass one argument: name of the C++ type to be displayed inside List')
            return
        typename = argv[0]
        # find the type and set it into global variable
        vtype = gdb.lookup_type(typename)
        ListPrinter.value_type = vtype

SetListType()