Help needed in this code while Stemming

#Stemming

from nltk.stem.porter import *
stemmer = PorterStemmer()

tokenized_tweet = tokenized_tweet.apply(lambda x: [stemmer.stem(i) for i in x]) # stemming
tokenized_tweet.head()

I’m getting the following error:
AttributeError Traceback (most recent call last)
in
4 stemmer = PorterStemmer()
5
----> 6 tokenized_tweet = tokenized_tweet.apply(lambda x: [stemmer.stem(doc) for doc in x]) # stemming
7 tokenized_tweet.head()

~\Anaconda3\lib\site-packages\pandas\core\series.py in apply(self, func, convert_dtype, args, **kwds)
3589 else:
3590 values = self.astype(object).values
-> 3591 mapped = lib.map_infer(values, f, convert=convert_dtype)
3592
3593 if len(mapped) and isinstance(mapped[0], Series):

pandas/_libs/lib.pyx in pandas._libs.lib.map_infer()

in (x)
4 stemmer = PorterStemmer()
5
----> 6 tokenized_tweet = tokenized_tweet.apply(lambda x: [stemmer.stem(doc) for doc in x]) # stemming
7 tokenized_tweet.head()

in (.0)
4 stemmer = PorterStemmer()
5
----> 6 tokenized_tweet = tokenized_tweet.apply(lambda x: [stemmer.stem(doc) for doc in x]) # stemming
7 tokenized_tweet.head()

~\Anaconda3\lib\site-packages\nltk\stem\porter.py in stem(self, word)
654
655 def stem(self, word):
–> 656 stem = word.lower()
657
658 if self.mode == self.NLTK_EXTENSIONS and word in self.pool:

AttributeError: ‘function’ object has no attribute ‘lower’