_nt_itemgetters = {}


def dictnamedtuple(typename, field_names, *, rename=False, defaults=None, module=None):
    from operator import itemgetter as _itemgetter, eq as _eq
    from keyword import iskeyword as _iskeyword
    from collections import OrderedDict
    import sys as _sys

    if isinstance(field_names, str):
        field_names = field_names.replace(',', ' ').split()
    field_names = list(map(str, field_names))
    typename = _sys.intern(str(typename))

    if rename:
        seen = set()
        for index, name in enumerate(field_names):
            if (not name.isidentifier()
                    or _iskeyword(name)
                    or name.startswith('_')
                    or name in seen):
                field_names[index] = f'_{index}'
            seen.add(name)

    for name in [typename] + field_names:
        if not isinstance(name, str):
            raise TypeError('Type names and field names must be strings')
        if not name.isidentifier():
            raise ValueError('Type names and field names must be valid '
                             f'identifiers: {name!r}')
        if _iskeyword(name):
            raise ValueError('Type names and field names cannot be a '
                             f'keyword: {name!r}')

    seen = set()
    for name in field_names:
        if name.startswith('_') and not rename:
            raise ValueError('Field names cannot start with an underscore: '
                             f'{name!r}')
        if name in seen:
            raise ValueError(f'Encountered duplicate field name: {name!r}')
        seen.add(name)

    field_defaults = {}
    if defaults is not None:
        defaults = tuple(defaults)
        if len(defaults) > len(field_names):
            raise TypeError('Got more default values than field names')
        field_defaults = dict(reversed(list(zip(reversed(field_names),
                                                reversed(defaults)))))

    # Variables used in the methods and docstrings
    field_names = tuple(map(_sys.intern, field_names))
    num_fields = len(field_names)
    arg_list = repr(field_names).replace("'", "")[1:-1]
    repr_fmt = '(' + ', '.join(f'{name}=%r' for name in field_names) + ')'
    tuple_new = tuple.__new__
    _len = len

    # Create all the named tuple methods to be added to the class namespace

    s = f'def __new__(_cls, {arg_list}): return _tuple_new(_cls, ({arg_list}))'
    namespace = {'_tuple_new': tuple_new, '__name__': f'namedtuple_{typename}'}
    # Note: exec() has the side-effect of interning the field names
    exec(s, namespace)
    __new__ = namespace['__new__']
    __new__.__doc__ = f'Create new instance of {typename}({arg_list})'
    if defaults is not None:
        __new__.__defaults__ = defaults

    @classmethod
    def _make(cls, iterable):
        result = tuple_new(cls, iterable)
        if _len(result) != num_fields:
            raise TypeError(f'Expected {num_fields} arguments, got {len(result)}')
        return result

    _make.__func__.__doc__ = (f'Make a new {typename} object from a sequence '
                              'or iterable')

    def _replace(_self, **kwds):
        result = _self._make(map(kwds.pop, field_names, _self))
        if kwds:
            raise ValueError(f'Got unexpected field names: {list(kwds)!r}')
        return result

    _replace.__doc__ = (f'Return a new {typename} object replacing specified '
                        'fields with new values')

    def __repr__(self):
        'Return a nicely formatted representation string'
        return self.__class__.__name__ + repr_fmt % self

    def _asdict(self):
        'Return a new OrderedDict which maps field names to their values.'
        return OrderedDict(zip(self._fields, self))

    def __getnewargs__(self):
        'Return self as a plain tuple.  Used by copy and pickle.'
        return tuple(self)

    # Modify function metadata to help with introspection and debugging

    for method in (__new__, _make.__func__, _replace,
                   __repr__, _asdict, __getnewargs__):
        method.__qualname__ = f'{typename}.{method.__name__}'

    # Build-up the class namespace dictionary
    # and use type() to build the result class
    class_namespace = {
        '__doc__': f'{typename}({arg_list})',
        '__slots__': (),
        '_fields': field_names,
        '_fields_defaults': field_defaults,
        '__new__': __new__,
        '_make': _make,
        '_replace': _replace,
        '__repr__': __repr__,
        '_asdict': _asdict,
        '__getnewargs__': __getnewargs__,
    }
    cache = _nt_itemgetters
    for index, name in enumerate(field_names):
        try:
            itemgetter_object, doc = cache[index]
        except KeyError:
            itemgetter_object = _itemgetter(index)
            doc = f'Alias for field number {index}'
            cache[index] = itemgetter_object, doc
        class_namespace[name] = property(itemgetter_object, doc=doc)

    result = type(typename, (tuple,), class_namespace)

    # For pickling to work, the __module__ variable needs to be set to the frame
    # where the named tuple is created.  Bypass this step in environments where
    # sys._getframe is not defined (Jython for example) or sys._getframe is not
    # defined for arguments greater than 0 (IronPython), or where the user has
    # specified a particular module.
    if module is None:
        try:
            module = _sys._getframe(1).f_globals.get('__name__', '__main__')
        except (AttributeError, ValueError):
            pass
    if module is not None:
        result.__module__ = module

    class DictNamedTuple(result):

        DictNamedTuple = True
        TypeName = typename

        def keys(self):
            keys = []
            for key in self._fields:
                keys.append(key)
            return keys

        def items(self):
            found = []
            for key in self._fields:
                value = getattr(self, key)
                found.append((key, value))
            return found

        def values(self):
            values = []
            for key in self._fields:
                values.append(getattr(self, key))
            return values

        def get(self, key):
            value = getattr(self, key)
            return value

        def __getitem__(self, item):
            if isinstance(item, str):
                item = self._fields.index(item)
            val = super(DictNamedTuple, self).__getitem__(item)
            return val

    return DictNamedTuple