use a defaultdict for blockinfo, which arose in review of PR #3232

this is to accomodate future population of blockinfo from multiple sources

how is this change tested? it *shouldn't* change anything. but scale_in is not well tested...

Author: benclifford

parsl/executors/high_throughput/executor.py

@@ -1,4 +1,5 @@
 import typing
+from collections import defaultdict
 from concurrent.futures import Future
 import typeguard
 import logging
@@ -730,13 +731,11 @@ class BlockInfo:
             idle: float  # shortest idle time of any manager in this block
 
         managers = self.connected_managers()
-        block_info: Dict[str, BlockInfo] = {}
+        block_info: Dict[str, BlockInfo] = defaultdict(lambda: BlockInfo(tasks=0, idle=float('inf')))
         for manager in managers:
             if not manager['active']:
                 continue
             b_id = manager['block_id']
-            if b_id not in block_info:
-                block_info[b_id] = BlockInfo(tasks=0, idle=float('inf'))
             block_info[b_id].tasks += manager['tasks']
             block_info[b_id].idle = min(block_info[b_id].idle, manager['idle_duration'])