REF: stronger typing in IntervalTree (pandas-dev#41814)

Author: jbrockmendel

pandas/_libs/intervaltree.pxi.in

@@ -31,7 +31,9 @@ cdef class IntervalTree(IntervalMixin):
     we are emulating the IndexEngine interface
     """
     cdef readonly:
-        object left, right, root, dtype
+        ndarray left, right
+        IntervalNode root
+        object dtype
         str closed
         object _is_overlapping, _left_sorter, _right_sorter
 
@@ -203,6 +205,41 @@ cdef sort_values_and_indices(all_values, all_indices, subset):
 # Nodes
 # ----------------------------------------------------------------------
 
+@cython.internal
+cdef class IntervalNode:
+    cdef readonly:
+        int64_t n_elements, n_center, leaf_size
+        bint is_leaf_node
+
+    def __repr__(self) -> str:
+        if self.is_leaf_node:
+            return (
+                f"<{type(self).__name__}: {self.n_elements} elements (terminal)>"
+            )
+        else:
+            n_left = self.left_node.n_elements
+            n_right = self.right_node.n_elements
+            n_center = self.n_elements - n_left - n_right
+            return (
+                f"<{type(self).__name__}: "
+                f"pivot {self.pivot}, {self.n_elements} elements "
+                f"({n_left} left, {n_right} right, {n_center} overlapping)>"
+            )
+
+    def counts(self):
+        """
+        Inspect counts on this node
+        useful for debugging purposes
+        """
+        if self.is_leaf_node:
+            return self.n_elements
+        else:
+            m = len(self.center_left_values)
+            l = self.left_node.counts()
+            r = self.right_node.counts()
+            return (m, (l, r))
+
+
 # we need specialized nodes and leaves to optimize for different dtype and
 # closed values
 
@@ -240,7 +277,7 @@ NODE_CLASSES = {}
 
 
 @cython.internal
-cdef class {{dtype_title}}Closed{{closed_title}}IntervalNode:
+cdef class {{dtype_title}}Closed{{closed_title}}IntervalNode(IntervalNode):
     """Non-terminal node for an IntervalTree
 
     Categorizes intervals by those that fall to the left, those that fall to
@@ -252,8 +289,6 @@ cdef class {{dtype_title}}Closed{{closed_title}}IntervalNode:
         int64_t[:] center_left_indices, center_right_indices, indices
         {{dtype}}_t min_left, max_right
         {{dtype}}_t pivot
-        int64_t n_elements, n_center, leaf_size
-        bint is_leaf_node
 
     def __init__(self,
                  ndarray[{{dtype}}_t, ndim=1] left,
@@ -381,31 +416,6 @@ cdef class {{dtype_title}}Closed{{closed_title}}IntervalNode:
             else:
                 result.extend(self.center_left_indices)
 
-    def __repr__(self) -> str:
-        if self.is_leaf_node:
-            return ('<{{dtype_title}}Closed{{closed_title}}IntervalNode: '
-                    '%s elements (terminal)>' % self.n_elements)
-        else:
-            n_left = self.left_node.n_elements
-            n_right = self.right_node.n_elements
-            n_center = self.n_elements - n_left - n_right
-            return ('<{{dtype_title}}Closed{{closed_title}}IntervalNode: '
-                    'pivot %s, %s elements (%s left, %s right, %s '
-                    'overlapping)>' % (self.pivot, self.n_elements,
-                                       n_left, n_right, n_center))
-
-    def counts(self):
-        """
-        Inspect counts on this node
-        useful for debugging purposes
-        """
-        if self.is_leaf_node:
-            return self.n_elements
-        else:
-            m = len(self.center_left_values)
-            l = self.left_node.counts()
-            r = self.right_node.counts()
-            return (m, (l, r))
 
 NODE_CLASSES['{{dtype}}',
              '{{closed}}'] = {{dtype_title}}Closed{{closed_title}}IntervalNode