We can remove elements using Element.remove(). Let’s say we want to remove all countries with a rank higher than 50:

>>>
>>> for country in root.findall('country'):
...     rank = int(country.find('rank').text)
...     if rank > 50:
...         root.remove(country)
...
>>> tree.write('output.xml')

When the original xml has over 2 country with  rank>50,and they are one by one neighborly siblings element,the upper code will delete the 1st 3rd 5th and more odd No. country.
A proper example should be:
index=0
while index < len(root.findall("./*")):
    rank = int (root[index].find("rank").text)
    if rank>50:
        root.remove(root[index])
        index=index+0
        continue
    index=index+1


I think "for each in list" should not work by index,but should work by pointer like thing,could be a list of pointers.
A finial solution should be like this --- when the "for each in list" was acting,the pointers list would be fixed,and you need not to worry about the "list" changing.