如何解决“'NoneType'类型的参数不可迭代”的问题？

Question

I tried to solve a Python exercise but my program blows up while runing.

The exercise instructions are:

Open the file romeo.txt and read it line by line. For each line, split the line into a list of words using the split() method. The program should build a list of words. For each word on each line check to see if the word is already in the list and if not append it to the list. When the program completes, sort and print the resulting words in alphabetical order.

Here is my code:

fname = input("Enter file name: ")
fh = open(fname)
j=-1
glolist=list()
for line in fh:
    line=line.rstrip()
    lst=line.split()
    nb=len(lst)
    i=0
    while i< nb:
        if lst[i] not in glolist:    #argument of type 'NoneType' is not iterable"
            i=i+1
        else:
            j=i
            i=i+1
    if j==-1:
        glolist=glolist+lst
    else:
        h=0
        while h<j:
            glolist=lst.append(lst[h])
            h=h+1
        h=h+1
        while h<nb:
            glolist=lst.append(lst[h])
            h=h+1
glolist=glolist.sort()
print(glolist)

Answer 1

fname = input("Enter file name: ")
fh = open(fname)
words=list()
for line in fh:
    line=line.rstrip()
    lst=line.split()
    i=0
    while i<len(lst):
        str=lst[i]
        if str in words:
            i=i+1
        else:
            words.append(str)
            i=i+1
words.sort()
print(words)