def _construct_key(previous_key, separator, new_key):
if previous_key:<EOL><INDENT>return u"<STR_LIT>".format(previous_key, separator, new_key)<EOL><DEDENT>else:<EOL><INDENT>return new_key<EOL><DEDENT>
Returns the new_key if no previous key exists, otherwise concatenates
previous key, separator, and new_key
:param previous_key:
:param separator:
:param new_key:
:return: a string if previous_key exists and simply passes through the
new_key otherwise