Add a method that return nodes and leaves (#27) (#30)

Add a test
Fix #27

stree/Strees.py

@@ -818,6 +818,23 @@ class Stree(BaseEstimator, ClassifierMixin):
         score = y_true == y_pred
         return _weighted_sum(score, sample_weight, normalize=True)
 
+    def nodes_leaves(self) -> tuple:
+        """Compute the number of nodes and leaves in the built tree
+
+        Returns
+        -------
+        [tuple]
+            tuple with the number of nodes and the number of leaves
+        """
+        nodes = 0
+        leaves = 0
+        for node in self:
+            if node.is_leaf():
+                leaves += 1
+            else:
+                nodes += 1
+        return nodes, leaves
+
     def __iter__(self) -> Siterator:
         """Create an iterator to be able to visit the nodes of the tree in
         preorder, can make a list with all the nodes in preorder

stree/tests/Stree_test.py

@@ -454,3 +454,22 @@ class Stree_test(unittest.TestCase):
         clf = Stree(random_state=self._random_state)
         clf.fit(X, y)
         self.assertEqual(7, clf.depth_)
+
+    def test_nodes_leaves(self):
+        X, y = load_dataset(
+            random_state=self._random_state,
+            n_classes=3,
+            n_features=5,
+            n_samples=1500,
+        )
+        clf = Stree(random_state=self._random_state)
+        clf.fit(X, y)
+        nodes, leaves = clf.nodes_leaves()
+        self.assertEqual(12, nodes)
+        self.assertEquals(13, leaves)
+        X, y = load_wine(return_X_y=True)
+        clf = Stree(random_state=self._random_state)
+        clf.fit(X, y)
+        nodes, leaves = clf.nodes_leaves()
+        self.assertEqual(8, nodes)
+        self.assertEquals(9, leaves)