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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _parse_attr(cls, value, package_dir=None):
 """Represents value as a module attribute. Examples: attr: package.attr attr: package.module.attr :param str value: :rtype: str """

        attr_directive = 'attr:'
        if not value.startswith(attr_directive):
            return value

        attrs_path = value.replace(attr_directive, '').strip().split('.')
        attr_name = attrs_path.pop()

        module_name = '.'.join(attrs_path)
        module_name = module_name or '__init__'

        parent_path = os.getcwd()
        if package_dir:
            if attrs_path[0] in package_dir:
                # A custom path was specified for the module we want to import
                custom_path = package_dir[attrs_path[0]]
                parts = custom_path.rsplit('/', 1)
                if len(parts) > 1:
                    parent_path = os.path.join(os.getcwd(), parts[0])
                    module_name = parts[1]
                else:
                    module_name = custom_path
            elif '' in package_dir:
                # A custom parent directory was specified for all root modules
                parent_path = os.path.join(os.getcwd(), package_dir[''])
        sys.path.insert(0, parent_path)
        try:
            module = import_module(module_name)
            value = getattr(module, attr_name)

        finally:
            sys.path = sys.path[1:]

        return value