(core) Update logging in sandbox code, and log tracebacks as single log messages.

Summary:
- Replace logger module by the standard module 'logging'.
- When a log message from the sandbox includes newlines (e.g. for tracebacks),
  keep those lines together in the Node log message.

  Previously each line was a different message, making it difficult to view
  tracebacks, particularly in prod where each line becomes a separate message
  object.

- Fix assorted lint errors.

Test Plan: Added a test for the log-line splitting and escaping logic.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3956

sandbox/grist/main.py

@@ -25,11 +25,20 @@ from acl_formula import parse_acl_formula
 from sandbox import get_default_sandbox
 from imports.register import register_import_parsers
 
-import logger
-log = logger.Logger(__name__, logger.INFO)
+# Handler for logging, which flushes each message.
+class FlushingStreamHandler(logging.StreamHandler):
+  def emit(self, record):
+    super(FlushingStreamHandler, self).emit(record)
+    self.flush()
 
-# Configure logging module to behave similarly to logger. (It may be OK to get rid of logger.)
-logging.basicConfig(format="[%(levelname)s] [%(name)s] %(message)s")
+# Configure logging module to produce messages with log level and logger name.
+logging.basicConfig(format="[%(levelname)s] [%(name)s] %(message)s",
+    handlers=[FlushingStreamHandler(sys.stderr)],
+    level=logging.INFO)
+
+# The default level is INFO. If a different level is desired, add a call like this:
+#   log.setLevel(logging.WARNING)
+log = logging.getLogger(__name__)
 
 def table_data_from_db(table_name, table_data_repr):
   if table_data_repr is None:
@@ -57,7 +66,7 @@ def run(sandbox):
     # Wrap each method so that it logs a message that it's being called.
     @functools.wraps(method)
     def wrapper(*args, **kwargs):
-      log.debug("calling %s" % method.__name__)
+      log.debug("calling %s", method.__name__)
       return method(*args, **kwargs)
 
     sandbox.register(method.__name__, wrapper)