You need to convert the dtype object
to unicode
string as is clearly mentioned in the traceback.
x = v.fit_transform(df['Review'].values.astype('U')) ## Even astype(str) would work
From the Doc page of TFIDF Vectorizer:
fit_transform(raw_documents, y=None)
Parameters: raw_documents : iterable
an iterable which yields either str, unicode or file objects