Hi. I think my code does the right thing, but it doesn't get accepted. Why that?

# E.g. word_count("I do not like it Sam I Am") gets back a dictionary like:
# {'i': 2, 'do': 1, 'it': 1, 'sam': 1, 'like': 1, 'not': 1, 'am': 1}
def word_count(aString):
    aString = aString.lower()
    word = ""
    word_list = []

    while True:
        if "  " in aString:
            aString = aString.replace("  ", " ")
        else:
            break

    if aString[-1] == " ":
        alist2 = list(aString)
        del alist2[-1]
        aString = "".join(alist2)

    if aString[0] == " ":
        alist2 = list(aString)
        del alist2[0]
        aString = "".join(alist2)

    for letter in aString:
        if letter != " ":
            word += letter
        else:
            word_list.append(word)
            word = ""
    word_list.append(word)

    word_count={}
    for word in word_list:
        if word not in word_count:
            word_count[word] = 1
        else:
            word_count[word] += 1
    return word_count