def __init__(self):
    """Create a sppasBaseSet instance."""
    self._data_set = collections.OrderedDict()

def get_value(self, data):
    """Return the string value corresponding to a data.

        :param data: (object)
        :returns: (list of str) the string value to associate to the data.

        """
    return self._data_set.get(data, None)

def append(self, data, value):
    """Append a data in the data set, with the given value.

        :param data: (object)
        :param value: (list of str) List of any string.

        """
    if value is None:
        raise sppasTypeError(value, 'list')
    if isinstance(value, list) is False:
        raise sppasTypeError(value, 'list')
    if data in self._data_set:
        old_value_list = self._data_set[data]
        self._data_set[data] = list(set(old_value_list + value))
    else:
        self._data_set[data] = value

def remove(self, data):
    """Remove the data of the data set.

        :param data: (object)

        """
    if data in self._data_set:
        del self._data_set[data]

def copy(self):
    """Make a deep copy of self."""
    d = sppasBaseSet()
    for data, value in self._data_set.items():
        d.append(data, value)
    return d

def __iter__(self):
    for data in list(self._data_set.keys()):
        yield data

def __len__(self):
    return len(self._data_set)

def __contains__(self, data):
    return data in self._data_set

def __eq__(self, other):
    """Check if data sets are equals, i.e. share the same data."""
    if len(self) != len(other):
        return False
    for key, value in self._data_set.items():
        if key not in other:
            return False
        other_value = other.get_value(key)
        if set(other_value) != set(value):
            return False
    return True

def __or__(self, other):
    """Implements the '|' operator between 2 data sets.

        The operator '|' does the intersection operation.

        """
    d = self.copy()
    for data in other:
        d.append(data, other.get_value(data))
    return d

def __and__(self, other):
    """Implements the '&' operator between 2 data sets.

        The operator '&' does the union operation.

        """
    d = sppasBaseSet()
    for data in self:
        if data in other:
            d.append(data, self.get_value(data))
            d.append(data, other.get_value(data))
    return d