Remove a tag using BeautifulSoup but keep its contents

The strategy I used is to replace a tag with its contents if they are of type NavigableString and if they aren't, then recurse into them and replace their contents with NavigableString, etc. Try this:

from BeautifulSoup import BeautifulSoup, NavigableString

def strip_tags(html, invalid_tags):
    soup = BeautifulSoup(html)

    for tag in soup.findAll(True):
        if tag.name in invalid_tags:
            s = ""

            for c in tag.contents:
                if not isinstance(c, NavigableString):
                    c = strip_tags(unicode(c), invalid_tags)
                s += unicode(c)

            tag.replaceWith(s)

    return soup

html = "<p>Good, <b>bad</b>, and <i>ug<b>l</b><u>y</u></i></p>"
invalid_tags = ['b', 'i', 'u']
print strip_tags(html, invalid_tags)

The result is:

<p>Good, bad, and ugly</p>

I gave this same answer on another question. It seems to come up a lot.

I have a simpler solution but I don't know if there's a drawback to it.

UPDATE: there's a drawback, see Jesse Dhillon's comment. Also, another solution will be to use Mozilla's Bleach instead of BeautifulSoup.

from BeautifulSoup import BeautifulSoup

VALID_TAGS = ['div', 'p']

value = '<div><p>Hello <b>there</b> my friend!</p></div>'

soup = BeautifulSoup(value)

for tag in soup.findAll(True):
    if tag.name not in VALID_TAGS:
        tag.replaceWith(tag.renderContents())

print soup.renderContents()

This will also print <div><p>Hello there my friend!</p></div> as desired.

Current versions of the BeautifulSoup library have an undocumented method on Tag objects called replaceWithChildren(). So, you could do something like this:

html = "<p>Good, <b>bad</b>, and <i>ug<b>l</b><u>y</u></i></p>"
invalid_tags = ['b', 'i', 'u']
soup = BeautifulSoup(html)
for tag in invalid_tags: 
    for match in soup.findAll(tag):
        match.replaceWithChildren()
print soup

Looks like it behaves like you want it to and is fairly straightforward code (although it does make a few passes through the DOM, but this could easily be optimized.)

Although this has already been mentoned by other people in the comments, I thought I'd post a full answer showing how to do it with Mozilla's Bleach. Personally, I think this is a lot nicer than using BeautifulSoup for this.

import bleach
html = "<b>Bad</b> <strong>Ugly</strong> <script>Evil()</script>"
clean = bleach.clean(html, tags=[], strip=True)
print clean # Should print: "Bad Ugly Evil()"