input: Write a function to construct an XML document in Python using the given list of items. The function should return the XML document as a string. If the input list is empty, the function should return an empty string.
  assert construct_xml(['Item1', 'Item2', 'Item3'])=='<data><item>Item1</item><item>Item2</item><item>Item3</item></data>'
  assert construct_xml([])==''
output: def construct_xml(items):
      if not items:
          return ''
      xml_items = ''.join(f'<item>{item}</item>' for item in items)
      return f'<data>{xml_items}</data>'