第一個situation：tag內有link

from lxml import etree 

node = etree.fromstring('<a xml = 'www.www.com'><c>bum</c></a>')

print node.findtext('c',default = 'what happened?')

第二個situation：所求text所在tag上一階tag無content

from lxml import etree 

node = etree.fromstring('<a><b><c>bum</c></b></a>')

print node.findtext('c', default = 'what happened?')

以上兩個situation所回傳的結果都是‘None’

成功的situation

from lxml import etree 

node = etree.fromstring('<a><c>bum</c></a>')

print node.findtext('c')

想問這兩個問題該怎麼解決？