I gave you the link to the documentation for
str
types earlier today. Many of the functions return a modified copy, but as you can see there is no specific copy method. But you have not explained where the error occurs.
[edit]
Take a look at the documentation at
NLTK :: nltk.classify.naivebayes[
^]. The
classify
method calls
prob_classify
passing in the parameter from your call. One of the next actions is to call
copy
on that parameter. But the
str
object does not have a
copy
method, as already shown. So the conclusion is that you are passing an invalid parameter to classify.
[/edit]