basic python questions

[nateastle at gmail.com]

I have a simple assignment for school but am unsure where to go. The
assignment is to read in a text file, split out the words and say which
line each word appears in alphabetical order. I have the basic outline
of the program done which is:

def Xref(filename):
    try:
        fp = open(filename, "r")
        lines = fp.readlines()
        fp.close()
    except:
        raise "Couldn't read input file \"%s\"" % filename
    dict = {}
    for line_num in xrange(len(lines)):
        if lines[line_num] == "":  continue
        words = lines[line_num].split()
        for word in words:
            if not dict.has_key(word):
                dict[word] = []
            if line_num+1 not in dict[word]:
                dict[word].append(line_num+1)
    return dict

My question is, how do I easily parse out punction marks and how do I
sort the list and if there anything else that I am doing wrong in this
code it would be much help.