从python编辑.js文件

Question

I'm writing a program that involves editing Firefox's proxy settings, specifically the socks and http proxy settings. I want to do this through editing Firefox's prefs.js file. It opens just fine in python - but after that I just can't think of a way to do this that isn't incredibly long and roundabout. The part of prefs.js that I want to edit looks like this:

user_pref("network.proxy.backup.ftp", "");
user_pref("network.proxy.backup.ftp_port", 0);
user_pref("network.proxy.backup.socks", "");
user_pref("network.proxy.backup.socks_port", 0);
user_pref("network.proxy.backup.ssl", "");
user_pref("network.proxy.backup.ssl_port", 0);
user_pref("network.proxy.ftp", "foo.bar");
user_pref("network.proxy.ftp_port", 5);
user_pref("network.proxy.gopher", "");
user_pref("network.proxy.gopher_port", 0);
user_pref("network.proxy.http", "foo.bar");
user_pref("network.proxy.http_port", 5);
user_pref("network.proxy.share_proxy_settings", true);
user_pref("network.proxy.socks", "foo.bar");
user_pref("network.proxy.socks_port", 5);
user_pref("network.proxy.ssl", "foo.bar");
user_pref("network.proxy.ssl_port", 5);
user_pref("network.proxy.type", 1);

Answer 1

You don't really need a JavaScript parser or anything fancy here; you could do this with very simple regular expressions. For example:

r = re.compile(r'user_pref\("network.proxy.socks", .*?\);')
with open('prefs.js') as f:
    contents = f.read()
contents = r.sub(r'user_pref("network.proxy.socks", "the.value.i.want");', 
                 contents)
with open('newprefs.js', 'w') as f:
    f.write(contents)

If you don't understand even simple regular expressions, this isn't too hard to do with trivial string manipulation either. For example:

with open('prefs.js') as fin, open('newprefs.js', 'w') as fout:
    for line in fin:
        if 'user_pref("network.proxy.socks",' in line:
            line = 'user_pref("network.proxy.socks", "the.value.i.want");\n'
        fout.write(line)

And to edit more lines, just do the same thing more times.