Add get_ngrams_length to SS3 class

This method can be used to return the length of longest learned n-gram.

pyss3/__init__.py

@@ -1066,6 +1066,15 @@ def get_most_probable_category(self):
         """
         return self.get_category_name(self.__get_most_probable_category__())
 
+    def get_ngrams_length(self):
+        """
+        Return the length of longest learned n-gram.
+
+        :returns: the length of longest learned n-gram.
+        :rtype: int
+        """
+        return len(self.__max_fr__[0]) if len(self.__max_fr__) > 0 else 0
+
     def get_category_index(self, name):
         """
         Given its name, return the category index.

tests/test_pyss3.py

@@ -253,6 +253,7 @@ def test_pyss3_ss3(mockers):
     assert clf.get_category_index("a_category") == IDX_UNKNOWN_CATEGORY
     assert clf.get_category_name(0) == STR_UNKNOWN_CATEGORY
     assert clf.get_category_name(-1) == STR_UNKNOWN_CATEGORY
+    assert clf.get_ngrams_length() == 0
 
     with pytest.raises(pyss3.EmptyModelError):
         clf.predict(x_test)
@@ -263,6 +264,8 @@ def test_pyss3_ss3(mockers):
     # cv_m=STR_NORM_GV_XAI, sn_m=STR_XAI
     clf.fit(x_train, y_train)
 
+    assert clf.get_ngrams_length() == 1
+
     perform_tests_with(clf, [.00114, .00295, 0, 0, 0, .00016, .01894, 8.47741])
     perform_tests_on(clf.cv, 0.4307)
     perform_tests_on(clf.gv, 0.2148)
@@ -309,6 +312,8 @@ def test_pyss3_ss3(mockers):
 
     clf.fit(x_train, y_train, n_grams=3)
 
+    assert clf.get_ngrams_length() == 3
+
     # update_values
     clf.set_l(.3)
     clf.update_values()