def add_filter_by_extension(self, extensions, filter_type=DefaultFilterType):
        """
        Add a files filter by extensions to this iterator.

        :param extensions: single extension or list of extensions to filter by.
                            for example: ["py", "js", "cpp", ...]
        """
        self.add_filter(FilterExtension(extensions), filter_type)
        return self
Add a files filter by extensions to this iterator.

        :param extensions: single extension or list of extensions to filter by.
                            for example: ["py", "js", "cpp", ...]