浮动”对象没有属性“降低” - python

我遇到此错误，我真的找不到原因。
有人可以指出原因吗？

for i in tweet_raw.comments:
    mns_proc.append(processComUni(i))

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-416-439073b420d1> in <module>()
      1 for i in tweet_raw.comments:
----> 2     tweet_processed.append(processtwt(i))
      3 

<ipython-input-414-4e1b8a8fb285> in processtwt(tweet)
      4     #Convert to lower case
      5     #tweet = re.sub('RT[\s]+','',tweet)
----> 6     tweet = tweet.lower()
      7     #Convert www.* or https?://* to URL
      8     #tweet = re.sub('((www\.[\s]+)|(https?://[^\s]+))','',tweet)

AttributeError: 'float' object has no attribute 'lower'

面临的第二个类似错误是:

for i in tweet_raw.comments:
    tweet_proc.append(processtwt(i))

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-423-439073b420d1> in <module>()
      1 for i in tweet_raw.comments:
----> 2     tweet_proc.append(processtwt(i))
      3 

<ipython-input-421-38fab2ef704e> in processComUni(tweet)
     11         tweet=re.sub(('[http]+s?://[^\s<>"]+|www\.[^\s<>"]+'),'', tweet)
     12     #Convert @username to AT_USER
---> 13     tweet = re.sub('@[^\s]+',' ',tweet)
     14     #Remove additional white spaces
     15     tweet = re.sub('[\s]+', ' ', tweet)

C:\Users\m1027201\AppData\Local\Continuum\Anaconda\lib\re.pyc in sub(pattern, repl, string, count, flags)
    149     a callable, it's passed the match object and must return
    150     a replacement string to be used."""
--> 151     return _compile(pattern, flags).sub(repl, string, count)
    152 
    153 def subn(pattern, repl, string, count=0, flags=0):

TypeError: expected string or buffer

在传递给processtwt()函数之前，我是否应该检查特定推文是否在发呆？对于这个错误，我什至不知道它在哪行失败。

python大神给出的解决方案

只需尝试使用此:
tweet = str(tweet).lower()

最近，我遇到了许多这样的错误，并将它们转换为字符串，然后再应用lower()始终对我有用。谢谢!