的所有子元素（后代）elem：
all_descendants = list(elem.iter())
一个更完整的示例：
>>> import xml.etree.ElementTree as ET
>>> a = ET.Element('a')
>>> b = ET.SubElement(a, 'b')
>>> c = ET.SubElement(a, 'c')
>>> d = ET.SubElement(a, 'd')
>>> e = ET.SubElement(b, 'e')
>>> f = ET.SubElement(d, 'f')
>>> g = ET.SubElement(d, 'g')
>>> [elem.tag for elem in a.iter()]
['a', 'b', 'e', 'c', 'd', 'f', 'g']
排除根本身：
>>> [elem.tag for elem in a.iter() if elem is not a]
['b', 'e', 'c', 'd', 'f', 'g']
602392714
清零编程群