Add MDC to the ButlerLogRecord definition

python/lsst/daf/butler/core/logging.py

@@ -25,7 +25,8 @@
 
 import logging
 import datetime
-from typing import List, Union, Optional, ClassVar, Iterable, Iterator
+from collections import defaultdict
+from typing import List, Union, Optional, ClassVar, Iterable, Iterator, Dict
 
 from logging import LogRecord, StreamHandler
 from pydantic import BaseModel, ValidationError
@@ -126,6 +127,7 @@ class ButlerLogRecord(BaseModel):
     funcName: Optional[str]
     process: int
     processName: str
+    MDC: Dict[str, str]
 
     class Config:
         allow_mutation = False
@@ -147,6 +149,14 @@ def from_record(cls, record: LogRecord) -> ButlerLogRecord:
 
         record_dict["message"] = record.getMessage()
 
+        # MDC
+        if hasattr(record, "MDC"):
+            # mypy does not understand hasattr.
+            record_dict["MDC"] = dict(record.MDC)  # type: ignore
+        else:
+            # Use an empty MDC to prevent format failures.
+            record_dict["MDC"] = defaultdict(str)
+
         # Always use UTC because in distributed systems we can't be sure
         # what timezone localtime is and it's easier to compare logs if
         # every system is using the same time.