How to delete an item in a list if it exists?

I am getting new_tag from a form text field with self.response.get("new_tag") and selected_tags from checkbox fields with

self.response.get_all("selected_tags")

I combine them like this:

tag_string = new_tag
new_tag_list = f1.striplist(tag_string.split(",") + selected_tags)

(f1.striplist is a function that strips white spaces inside the strings in the list.)

But in the case that tag_list is empty (no new tags are entered) but there are some selected_tags, new_tag_list contains an empty string " ".

For example, from logging.info:

new_tag
selected_tags[u'Hello', u'Cool', u'Glam']
new_tag_list[u'', u'Hello', u'Cool', u'Glam']

How do I get rid of the empty string?

If there is an empty string in the list:

>>> s = [u'', u'Hello', u'Cool', u'Glam']
>>> i = s.index("")
>>> del s[i]
>>> s
[u'Hello', u'Cool', u'Glam']

But if there is no empty string:

>>> s = [u'Hello', u'Cool', u'Glam']
>>> if s.index(""):
        i = s.index("")
        del s[i]
    else:
        print "new_tag_list has no empty string"

But this gives:

Traceback (most recent call last):
  File "<pyshell#30>", line 1, in <module>
    if new_tag_list.index(""):
        ValueError: list.index(x): x not in list

Why does this happen, and how do I work around it?