pretty-printer for std::unique_ptr enabled for recursive printing

uptr_pretty_printer.py

class MUniquePointerPrinter:
    """ Print a unique_ptr with pointed-to-value
        credits: https://gcc.gnu.org/ml/libstdc++/2013-04/msg00098.html 
    """

    def __init__ (self, typename, val):
        self.val = val

    def to_string (self):
        v = self.val['_M_t']['_M_head_impl']
        return ('std::unique_ptr<%s> containing %s' % (str(v.type.target()),
                                                       str(v)))
    def children (self):
        l_address = self.val['_M_t']['_M_head_impl']
        l_value = 'NULL' if l_address == 0 else l_address.dereference ()
        return iter([('<managed value>', l_value)])