python小工具-将句子按单词转成列表

#将句子按单词转成列表
def myfunc(str):
    s=str.lower()
    myls=list()
    word=""
    for ch in s:
        if(ch==" "):
            if(word!=""):myls.append(word)
            word=""
        elif((ch>='a')&(ch<='z')):
            word+=ch
        elif((ch=='-')|(ch=="'")):
            word+=ch
        else:
            continue
    if(word!=""):myls.append(word)
    return myls