Add __len__ method to Index (#207)

* Add __len__ method to Index

* Deprecate get_size()

rtree/index.py

@@ -2,6 +2,7 @@
 import os
 import os.path
 import pprint
+import warnings
 
 from . import core
 
@@ -289,6 +290,18 @@ def __init__(self, *args, **kwargs):
                     self.insert(*item)
 
     def get_size(self):
+        warnings.warn(
+            "index.get_size() is deprecated, use len(index) instead",
+            DeprecationWarning,
+        )
+        return len(self)
+
+    def __len__(self):
+        """The number of entries in the index.
+
+        :return: number of entries
+        :rtype: int
+        """
         try:
             return self.count(self.bounds)
         except core.RTreeError:

tests/test_index.py

@@ -45,6 +45,22 @@ def test_libsidx_version(self):
         self.assertTrue(index.minor_version >= 7)
 
 
+class IndexCount(unittest.TestCase):
+
+    def setUp(self):
+        self.boxes15 = np.genfromtxt('boxes_15x15.data')
+        self.idx = index.Index()
+        for i, coords in enumerate(self.boxes15):
+            self.idx.add(i, coords)
+
+    def test_len(self):
+        self.assertEqual(len(self.idx), len(self.boxes15))
+
+    def test_get_size(self):
+        with pytest.deprecated_call():
+            self.assertEqual(self.idx.get_size(), len(self.boxes15))
+
+
 class IndexBounds(unittest.TestCase):
 
     def test_invalid_specifications(self):