Fix some linting issues.

pytato/analysis/__init__.py

@@ -26,7 +26,7 @@
 """
 
 from typing import (Mapping, Dict, Union, Set, Tuple, Any, FrozenSet,
-                    TYPE_CHECKING)
+                    Type, TYPE_CHECKING)
 from pytato.array import (Array, IndexLambda, Stack, Concatenate, Einsum,
                           DictOfNamedArrays, NamedArray,
                           IndexBase, IndexRemappingBase, InputArgumentBase,
@@ -426,18 +426,24 @@ class NodeTypeCountMapper(CachedWalkMapper):
     """
 
     def __init__(self) -> None:
+        from collections import defaultdict
         super().__init__()
-        self.counts = {}
+        self.counts = defaultdict(int)
 
     def get_cache_key(self, expr: ArrayOrNames) -> int:
         return id(expr)
 
     def post_visit(self, expr: Any) -> None:
+        if type(expr) not in self.counts:
+            self.counts[type(expr)] = 0
         self.counts[type(expr)] += 1
 
 
-def get_num_node_types(outputs: Union[Array, DictOfNamedArrays]) -> int:
-    """Returns the number of nodes of each given type in DAG *outputs*."""
+def get_num_node_types(outputs: Union[Array, DictOfNamedArrays]) -> Dict[Type, int]:
+    """
+    Returns a dictionary mapping node types to node count for that type
+    in DAG *outputs*.
+    """
 
     from pytato.codegen import normalize_outputs
     outputs = normalize_outputs(outputs)