You can decode the cssText in ASCII using the function sheet.cssText.decode('ascii') before writing to CSS file

# -*- coding: utf-8 -*-
import cssutils

css = '''/* a comment */
    .chat {
        background: #fff;
        color: white;
    }

    .chat-history {
        height: 100px;
        padding: 8px 24px;
        overflow-y: scroll;
    }
#live-chat header {
    background: #293239;
    border-radius: 5px 5px 0 0;
    color: #fff;
    cursor: pointer;
    padding: 16px 24px;
}
'''
sheet = cssutils.parseString(css)

for rule in sheet:
    if rule.type == rule.STYLE_RULE:
        # find property
        for property in rule.style:
            if property.name == 'color':
                property.value = 'green'
                property.priority = 'IMPORTANT'
                break
        # or simply:
        rule.style['margin'] = '01.0eM' # or: ('1em', 'important')


# cssutils.ser.prefs.resolveVariables == True since 0.9.7b2
cssTextDecoded = sheet.cssText.decode('ascii')
print(cssTextDecoded)
with open("hello.css", 'w') as f:
    f.write(cssTextDecoded)

You can try this:

print '<![if !IE]>  <link href="../styles/screen.css" rel="stylesheet" type="text/css" media="screen" /> <![endif]>\n'

You can't use python to run in the browser on the client's machine in the same way as JS, just because browsers are built to execute JS and not Python. However if all you want to do in the python is backend work, that is definitely possible.

I would suggest looking at Flask a popular python web framework that is quite easy to get started with.

Sven's answer helped me, but it didn't work out of the box. The following did it for me:

import bs4   #BeautifulSoup 3 has been replaced
soup = bs4.BeautifulSoup(open("index.html").read())
stylesheets = soup.findAll("link", {"rel": "stylesheet"})
for s in stylesheets:
    t = soup.new_tag('style')
    c = bs4.element.NavigableString(open(s["href"]).read())
    t.insert(0,c)
    t['type'] = 'text/css'
    s.replaceWith(t)
open("output.html", "w").write(str(soup))