Depth First Traversal on BeautifulSoup Parse Tree

问题

Is there a way to do a DFT on a BeautifulSoup parse tree? I'm trying to do something like starting at the root, usually , get all the child elements and then for each child element get their children, etc until I hit a terminal node at which point I'll build my way back up the tree. Problem is I can't seem to find a method that will allow me to do this. I found the findChildren method but that seems to just put the entire page in a list multiple times with each subsequent entry getting reduced. I might be able to use this to do a traversal however other than the last entry in the list it doesn't appear there is any way to identify entries as terminal nodes or not. Any ideas?

回答1:

recursiveChildGenerator() already does that:

soup = BeautifulSoup.BeautifulSoup(html)
for child in soup.recursiveChildGenerator():
     name = getattr(child, "name", None)
     if name is not None:
         print name
     elif not child.isspace(): # leaf node, don't print spaces
         print child

Output

For the html from @msalvadores's answer:

html
ul
li
Lorem ipsum dolor sit amet, consectetuer adipiscing elit.
li
Aliquam tincidunt mauris eu risus.
li
Vestibulum auctor dapibus neque.
html

NOTE: html is printed twice due to the example contains two opening <html> tags.

回答2:

I think you can use the method "childGenerator" and recursively use this one to parse the tree in a DFT fashion.

def recursiveChildren(x):
   if "childGenerator" in dir(x):
      for child in x.childGenerator():
          name = getattr(child, "name", None)
          if name is not None:
             print "[Container Node]",child.name
          recursiveChildren(child)
    else:
       if not x.isspace(): #Just to avoid printing "\n" parsed from document.
          print "[Terminal Node]",x

if __name__ == "__main__":
    soup = BeautifulSoup(your_data)
    for child in soup.childGenerator():
        recursiveChildren(child)

With "childGenerator" in dir(x) we make sure that an element is a container, terminal nodes such as NavigableStrings are not containers and do not contain children.

For some example HTML like:

<html>
<ul>
   <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
   <li>Aliquam tincidunt mauris eu risus.</li>
   <li>Vestibulum auctor dapibus neque.</li>
</ul>
</html>

This scripts prints ...

[Container Node] ul
[Container Node] li
[Terminal Node] Lorem ipsum dolor sit amet, consectetuer adipiscing elit.
[Container Node] li
[Terminal Node] Aliquam tincidunt mauris eu risus.
[Container Node] li
[Terminal Node] Vestibulum auctor dapibus neque.

来源：https://stackoverflow.com/questions/4814317/depth-first-traversal-on-beautifulsoup-parse-tree

标签

python

beautifulsoup

tree-traversal