diff --git a/app/server/lib/NSandbox.ts b/app/server/lib/NSandbox.ts
index 656e8216..ad31b8e4 100644
--- a/app/server/lib/NSandbox.ts
+++ b/app/server/lib/NSandbox.ts
@@ -279,7 +279,7 @@ export class NSandbox implements ISandbox {
     if (!this._streamToSandbox) {
       throw new Error('expected streamToSandbox to be configured');
     }
-    const sandboxStderrLogger = sandboxUtil.makeLinePrefixer('Sandbox stderr: ', this._logMeta);
+    const sandboxStderrLogger = sandboxUtil.makeLogLinePrefixer('Sandbox stderr: ', this._logMeta);
     this.childProc.stderr!.on('data', data => {
       this._lastStderr = data;
       sandboxStderrLogger(data);
diff --git a/app/server/lib/sandboxUtil.ts b/app/server/lib/sandboxUtil.ts
index 80211c55..a24af98a 100644
--- a/app/server/lib/sandboxUtil.ts
+++ b/app/server/lib/sandboxUtil.ts
@@ -33,16 +33,32 @@ export const EXC = false;
  * Binary data is encoded as with JSON.stringify.
  */
 export function makeLinePrefixer(prefix: string, logMeta: object) {
+  return _makeLinePrefixer(prefix, logMeta, text => text.indexOf('\n'));
+}
+
+/**
+ * Same as makeLinePrefixer, but avoids splitting lines except when a line starts with '[', since
+ * the sandbox prefixes all log messages with "[LEVEL]" prefix.
+ */
+export function makeLogLinePrefixer(prefix: string, logMeta: object) {
+  return _makeLinePrefixer(prefix, logMeta, text => {
+    const newline = text.indexOf("\n[");
+    // If no next log message, split at the last newline. Any earlier newlines would be included.
+    return (newline !== -1) ? newline : text.lastIndexOf("\n");
+  });
+}
+
+function _makeLinePrefixer(prefix: string, logMeta: object, findLineEnd: (text: string) => number) {
   let partial = '';
   return (data: Uint8Array) => {
     partial += MemBuffer.arrayToString(data);
     let newline;
-    while ((newline = partial.indexOf("\n")) !== -1) {
+    while (partial && (newline = findLineEnd(partial)) !== -1) {
       const line = partial.slice(0, newline);
       partial = partial.slice(newline + 1);
       // Escape some parts of the string by serializing it to JSON (without the quotes).
       log.origLog('info', "%s%s", prefix,
-        JSON.stringify(line).slice(1, -1).replace(/\\"/g, '"').replace(/\\\\/g, '\\'),
+        JSON.stringify(line).slice(1, -1).replace(/\\(['"\\])/g, '$1').replace(/\\n/g, '\n'),
         logMeta);
     }
   };
diff --git a/sandbox/grist/acl.py b/sandbox/grist/acl.py
index c73b4161..dcba9c0f 100644
--- a/sandbox/grist/acl.py
+++ b/sandbox/grist/acl.py
@@ -3,13 +3,13 @@
 # and to produce the ActionBundles expected by other code.
 
 import json
+import logging
 
 from acl_formula import parse_acl_grist_entities, parse_acl_formula_json
 import action_obj
-import logger
 import textbuilder
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class Permissions(object):
@@ -68,7 +68,7 @@ def prepare_acl_table_renames(docmodel, useractions, table_renames_dict):
           rule_info["tableId"] = table_renames_dict[rule_info.get("tableId")]
           rule_updates.append((rule_rec, {'userAttributes': json.dumps(rule_info)}))
       except Exception as e:
-        log.warn("Error examining aclRule: %s" % (e,))
+        log.warning("Error examining aclRule: %s", e)
 
   def do_renames():
     useractions.doBulkUpdateFromPairs('_grist_ACLResources', resource_updates)
@@ -104,7 +104,7 @@ def prepare_acl_col_renames(docmodel, useractions, col_renames_dict):
           rule_info["lookupColId"] = new_col_id
           rule_updates.append((rule_rec, {'userAttributes': json.dumps(rule_info)}))
       except Exception as e:
-        log.warn("Error examining aclRule: %s" % (e,))
+        log.warning("Error examining aclRule: %s", e)
 
   # Go through again checking if anything in ACL formulas is affected by the rename.
   for rule_rec in docmodel.aclRules.all:
diff --git a/sandbox/grist/codebuilder.py b/sandbox/grist/codebuilder.py
index 30224a0a..26212c65 100644
--- a/sandbox/grist/codebuilder.py
+++ b/sandbox/grist/codebuilder.py
@@ -2,6 +2,7 @@ import ast
 import contextlib
 import itertools
 import linecache
+import logging
 import re
 import textwrap
 
@@ -11,8 +12,7 @@ import six
 
 import friendly_errors
 import textbuilder
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 DOLLAR_REGEX = re.compile(r'\$(?=[a-zA-Z_][a-zA-Z_0-9]*)')
diff --git a/sandbox/grist/column.py b/sandbox/grist/column.py
index c0ba8906..ec5c6580 100644
--- a/sandbox/grist/column.py
+++ b/sandbox/grist/column.py
@@ -1,4 +1,5 @@
 import json
+import logging
 import types
 from collections import namedtuple
 from numbers import Number
@@ -11,10 +12,9 @@ import usertypes
 import relabeling
 import relation
 import moment
-import logger
 from sortedcontainers import SortedListWithKey
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 MANUAL_SORT = 'manualSort'
 MANUAL_SORT_COL_INFO = {
diff --git a/sandbox/grist/docactions.py b/sandbox/grist/docactions.py
index 592cb6c7..bc417edd 100644
--- a/sandbox/grist/docactions.py
+++ b/sandbox/grist/docactions.py
@@ -1,11 +1,11 @@
+import logging
 import six
 
 import actions
-import logger
 import schema
 from objtypes import strict_equal
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class DocActions(object):
   def __init__(self, engine):
diff --git a/sandbox/grist/engine.py b/sandbox/grist/engine.py
index c5ddf87d..15b70de8 100644
--- a/sandbox/grist/engine.py
+++ b/sandbox/grist/engine.py
@@ -4,6 +4,7 @@ The data engine ties the code generated from the schema with the document data,
 dependency tracking.
 """
 import itertools
+import logging
 import re
 import rlcompleter
 import sys
@@ -13,7 +14,7 @@ from collections import namedtuple, OrderedDict, defaultdict
 
 import six
 from six.moves import zip
-from six.moves.collections_abc import Hashable  # pylint:disable-all
+from six.moves.collections_abc import Hashable  # pylint:disable=import-error,no-name-in-module
 from sortedcontainers import SortedSet
 
 import acl
@@ -26,7 +27,6 @@ import docactions
 import docmodel
 from fake_std_streams import FakeStdStreams
 import gencode
-import logger
 import match_counter
 import objtypes
 from objtypes import strict_equal
@@ -40,7 +40,7 @@ import useractions
 import column
 import urllib_patch  # noqa imported for side effect # pylint:disable=unused-import
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 if six.PY2:
   reload(sys)
@@ -451,7 +451,7 @@ class Engine(object):
     if n:
       matched_cols = matched_cols[:n]
 
-    log.info('Found column from values in %.3fs' % (time.time() - start_time))
+    log.info('Found column from values in %.3fs', time.time() - start_time)
     return [c[1] for c in matched_cols]
 
   def assert_schema_consistent(self):
@@ -495,9 +495,9 @@ class Engine(object):
     self.dump_recompute_map()
 
   def dump_recompute_map(self):
-    log.debug("Recompute map (%d nodes):" % len(self.recompute_map))
+    log.debug("Recompute map (%d nodes):", len(self.recompute_map))
     for node, dirty_rows in six.iteritems(self.recompute_map):
-      log.debug("  Node %s: %s" % (node, dirty_rows))
+      log.debug("  Node %s: %s", node, dirty_rows)
 
   def _use_node(self, node, relation, row_ids=[]):
     # This is used whenever a formula accesses any part of any record. It's hot code, and
@@ -849,7 +849,7 @@ class Engine(object):
           is_first = node not in self._is_node_exception_reported
           if is_first:
             self._is_node_exception_reported.add(node)
-            log.info(value.details)
+            log.info("Formula error in %s: %s", node, value.details)
             # strip out details after logging
             value = objtypes.RaisedException(value.error, user_input=value.user_input)
 
@@ -1304,7 +1304,7 @@ class Engine(object):
       # If we get an exception, we should revert all changes applied so far, to keep things
       # consistent internally as well as with the clients and database outside of the sandbox
       # (which won't see any changes in case of an error).
-      log.info("Failed to apply useractions; reverting: %r" % (e,))
+      log.info("Failed to apply useractions; reverting: %r", e)
       self._undo_to_checkpoint(checkpoint)
 
       # Check schema consistency again. If this fails, something is really wrong (we tried to go
@@ -1313,7 +1313,7 @@ class Engine(object):
         if self._schema_updated:
           self.assert_schema_consistent()
       except Exception:
-        log.error("Inconsistent schema after revert on failure: %s" % traceback.format_exc())
+        log.error("Inconsistent schema after revert on failure: %s", traceback.format_exc())
 
       # Re-raise the original exception
       # In Python 2, 'raise' raises the most recent exception,
@@ -1354,7 +1354,7 @@ class Engine(object):
     Applies a single user action to the document, without running any triggered updates.
     A UserAction is a tuple whose first element is the name of the action.
     """
-    log.debug("applying user_action %s" % (user_action,))
+    log.debug("applying user_action %s", user_action)
     return getattr(self.user_actions, user_action.__class__.__name__)(*user_action)
 
   def apply_doc_action(self, doc_action):
@@ -1362,7 +1362,6 @@ class Engine(object):
     Applies a doc action, which is a step of a user action. It is represented by an Action object
     as defined in actions.py.
     """
-    #log.warn("Engine.apply_doc_action %s" % (doc_action,))
     self._gone_columns = []
 
     action_name = doc_action.__class__.__name__
@@ -1385,7 +1384,7 @@ class Engine(object):
         try:
           self.rebuild_usercode()
         except Exception:
-          log.error("Error rebuilding usercode after restoring schema: %s" % traceback.format_exc())
+          log.error("Error rebuilding usercode after restoring schema: %s", traceback.format_exc())
 
       # Re-raise the original exception
       # In Python 2, 'raise' raises the most recent exception,
@@ -1524,7 +1523,7 @@ class Engine(object):
     if new_checkpoint != checkpoint:
       (len_calc, len_stored, len_undo, len_ret) = checkpoint
       undo_actions = self.out_actions.undo[len_undo:]
-      log.info("Reverting %d doc actions" % len(undo_actions))
+      log.info("Reverting %d doc actions", len(undo_actions))
       self.user_actions.ApplyUndoActions([actions.get_action_repr(a) for a in undo_actions])
       del self.out_actions.calc[len_calc:]
       del self.out_actions.stored[len_stored:]
diff --git a/sandbox/grist/gencode.py b/sandbox/grist/gencode.py
index ed6a47ba..3042f076 100644
--- a/sandbox/grist/gencode.py
+++ b/sandbox/grist/gencode.py
@@ -15,7 +15,7 @@ The schema for grist data is:
     "formula": <opt_string>,
   }
 """
-import linecache
+import logging
 import re
 import imp
 from collections import OrderedDict
@@ -28,8 +28,7 @@ import summary
 import table
 import textbuilder
 from usertypes import get_type_default
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 indent_str = "  "
 
diff --git a/sandbox/grist/identifiers.py b/sandbox/grist/identifiers.py
index e4b847f0..c29ccd0d 100644
--- a/sandbox/grist/identifiers.py
+++ b/sandbox/grist/identifiers.py
@@ -3,6 +3,7 @@
 A module for creating and sanitizing identifiers
 """
 import itertools
+import logging
 import re
 import unicodedata
 from keyword import iskeyword
@@ -10,9 +11,7 @@ from string import ascii_uppercase
 
 import six
 
-import logger
-
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 _invalid_ident_char_re = re.compile(r'[^a-zA-Z0-9_]+')
 _invalid_ident_start_re = re.compile(r'^(?=[0-9_])')
diff --git a/sandbox/grist/import_actions.py b/sandbox/grist/import_actions.py
index b458f156..bc588fe7 100644
--- a/sandbox/grist/import_actions.py
+++ b/sandbox/grist/import_actions.py
@@ -1,10 +1,10 @@
+import logging
 from six.moves import zip
 
 import column
 import identifiers
-import logger
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 # Prefix for transform columns created during imports.
 _import_transform_col_prefix = 'gristHelper_Import_'
@@ -133,11 +133,11 @@ class ImportActions(object):
     tables = self._docmodel.tables
     hidden_table_rec = tables.lookupOne(tableId=hidden_table_id)
     src_cols = {c.colId for c in hidden_table_rec.columns}
-    log.debug("destCols:" + repr(transform_rule['destCols']))
+    log.debug("destCols: %r", transform_rule['destCols'])
 
     dest_cols = transform_rule['destCols']
 
-    log.debug("_MakeImportTransformColumns: {}".format("gen_all" if gen_all else "optimize"))
+    log.debug("_MakeImportTransformColumns: %s", "gen_all" if gen_all else "optimize")
 
     # Calling rebuild_usercode once per added column is wasteful and can be very slow.
     self._engine._should_rebuild_usercode = False
diff --git a/sandbox/grist/imports/import_csv.py b/sandbox/grist/imports/import_csv.py
index d3e80ee2..f35498c3 100644
--- a/sandbox/grist/imports/import_csv.py
+++ b/sandbox/grist/imports/import_csv.py
@@ -14,6 +14,7 @@ from imports import import_utils
 
 
 log = logging.getLogger(__name__)
+log.setLevel(logging.WARNING)
 
 SCHEMA = [
           {
diff --git a/sandbox/grist/imports/import_xls.py b/sandbox/grist/imports/import_xls.py
index 0b525e92..bd0a35e6 100644
--- a/sandbox/grist/imports/import_xls.py
+++ b/sandbox/grist/imports/import_xls.py
@@ -4,16 +4,17 @@ and returns a object formatted so that it can be used by grist for a bulk add re
 """
 import logging
 
-import six
 import openpyxl
 from openpyxl.utils.datetime import from_excel
-from openpyxl.worksheet import _reader
+from openpyxl.worksheet import _reader    # pylint:disable=no-name-in-module
+import six
 from six.moves import zip
 
 import parse_data
 from imports import import_utils
 
 log = logging.getLogger(__name__)
+log.setLevel(logging.WARNING)
 
 
 # Some strange Excel files have values that are marked as dates but are invalid as dates.
diff --git a/sandbox/grist/logger.py b/sandbox/grist/logger.py
deleted file mode 100644
index 6b3e9969..00000000
--- a/sandbox/grist/logger.py
+++ /dev/null
@@ -1,74 +0,0 @@
-"""
-Logging for code running in the sandbox. The output simply goes to stderr (which gets to the
-console of the Node process), but the levels allow some configuration.
-
-We don't use the `logging` module because it assumes more about the `time` module than we have.
-
-Usage:
-  import logger
-  log = logger.Logger(__name__, logger.DEBUG)    # Or logger.WARN; default is logger.INFO.
-  log.info("Hello world")
-      -> produces "[I] [foo.bar] Hello world"
-"""
-
-import sys
-
-# Level definitions
-DEBUG = 10
-INFO = 20
-WARN = 30
-ERROR = 40
-CRITICAL = 50
-
-# Level strings
-level_strings = {
-  DEBUG: 'DEBUG',
-  INFO: 'INFO',
-  WARN: 'WARN',
-  ERROR: 'ERROR',
-  CRITICAL: 'CRITICAL',
-}
-
-def log_stderr(level, name, msg):
-  sys.stderr.write("[%s] [%s] %s\n" % (level_strings.get(level, '?'), name, msg))
-  sys.stderr.flush()
-
-_log_handler = log_stderr
-
-def set_handler(log_handler):
-  """
-  Allows overriding the handler for all log messages. The handler should be a function, called as
-  log_handler(level, name, message).
-  Returns the handler which was set previously.
-  """
-
-  global _log_handler # pylint: disable=global-statement
-  prev = _log_handler
-  _log_handler = log_handler
-  return prev
-
-
-class Logger(object):
-  """
-  The object that actually provides the logging interface, specifically the methods debug, info,
-  warn, error, and critical. The constructor takes an argument for a name that gets included in
-  each message, and a minimum level, below which messages get ignored.
-  """
-  def __init__(self, name, min_level=INFO):
-    self._name = name
-    self._min_level = min_level
-
-  def _log(self, level, msg):
-    if level >= self._min_level:
-      _log_handler(level, self._name, msg)
-
-  def debug(self, msg):
-    self._log(DEBUG, msg)
-  def info(self, msg):
-    self._log(INFO, msg)
-  def warn(self, msg):
-    self._log(WARN, msg)
-  def error(self, msg):
-    self._log(ERROR, msg)
-  def critical(self, msg):
-    self._log(CRITICAL, msg)
diff --git a/sandbox/grist/lookup.py b/sandbox/grist/lookup.py
index 96683d8d..9dd7a19b 100644
--- a/sandbox/grist/lookup.py
+++ b/sandbox/grist/lookup.py
@@ -1,4 +1,5 @@
 import itertools
+import logging
 from abc import abstractmethod
 
 import six
@@ -11,8 +12,7 @@ import twowaymap
 import usertypes
 from functions.lookup import _Contains
 
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 def _extract(cell_value):
diff --git a/sandbox/grist/main.py b/sandbox/grist/main.py
index 952efd66..03968120 100644
--- a/sandbox/grist/main.py
+++ b/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)
diff --git a/sandbox/grist/migrations.py b/sandbox/grist/migrations.py
index 796470cb..419b9f1b 100644
--- a/sandbox/grist/migrations.py
+++ b/sandbox/grist/migrations.py
@@ -1,4 +1,6 @@
+# pylint:disable=too-many-lines
 import json
+import logging
 import re
 from collections import defaultdict
 
@@ -10,10 +12,9 @@ import identifiers
 import schema
 import summary
 import table_data_set
-import logger
 from column import is_visible_column
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 # PHILOSOPHY OF MIGRATIONS.
 #
@@ -388,8 +389,8 @@ def migration7(tdset):
     new_name = summary.encode_summary_table_name(source_table_name, groupby_col_ids)
     new_name = identifiers.pick_table_ident(new_name, avoid=table_name_set)
     table_name_set.add(new_name)
-    log.warn("Upgrading summary table %s for %s(%s) to %s" % (
-      t.tableId, source_table_name, groupby_colrefs, new_name))
+    log.warning("Upgrading summary table %s for %s(%s) to %s",
+      t.tableId, source_table_name, groupby_colrefs, new_name)
 
     # Remove the "lookupOrAddDerived" column from the source table (which is named using the
     # summary table name for its colId).
@@ -418,7 +419,7 @@ def migration7(tdset):
         groupby_cols.add(sum_col)
         source_cols.append((sum_col, src_col.id))
       else:
-        log.warn("Upgrading summary table %s: couldn't find column %s" % (t.tableId, col_ref))
+        log.warning("Upgrading summary table %s: couldn't find column %s", t.tableId, col_ref)
 
     # Finally, we have to remove all non-formula columns that are not groupby-columns (e.g.
     # 'manualSort'), because the new approach assumes ALL non-formula columns are for groupby.
@@ -1050,8 +1051,8 @@ def migration31(tdset):
       continue
     new_name = identifiers.pick_table_ident(new_name, avoid=table_name_set)
     table_name_set.add(new_name)
-    log.warn("Upgrading summary table %s for %s(%s) to %s" % (
-      t.tableId, source_table.tableId, groupby_col_ids, new_name))
+    log.warning("Upgrading summary table %s for %s(%s) to %s",
+      t.tableId, source_table.tableId, groupby_col_ids, new_name)
 
     # Schedule a rename of the summary table.
     table_renames.append((t, new_name))
diff --git a/sandbox/grist/parse_data.py b/sandbox/grist/parse_data.py
index 133d091a..b9d74130 100644
--- a/sandbox/grist/parse_data.py
+++ b/sandbox/grist/parse_data.py
@@ -15,6 +15,7 @@ import six
 from six.moves import zip, xrange
 
 log = logging.getLogger(__name__)
+log.setLevel(logging.WARNING)
 
 
 # Typecheck using type(value) instead of isinstance(value, some_type) makes parsing 25% faster
diff --git a/sandbox/grist/sandbox.py b/sandbox/grist/sandbox.py
index ff9727e2..db37c317 100644
--- a/sandbox/grist/sandbox.py
+++ b/sandbox/grist/sandbox.py
@@ -10,10 +10,13 @@ Usage:
 """
 
 import os
+import logging
 import marshal
 import sys
 import traceback
 
+log = logging.getLogger(__name__)
+
 class CarefulReader(object):
   """
   Wrap a pipe when reading from Pyodide, to work around marshaling
@@ -40,9 +43,6 @@ class CarefulReader(object):
   def __getattr__(self, attr):
     return getattr(self._file, attr)
 
-def log(msg):
-  sys.stderr.write(str(msg) + "\n")
-  sys.stderr.flush()
 
 class Sandbox(object):
   """
@@ -93,6 +93,7 @@ class Sandbox(object):
 
   @classmethod
   def use_pyodide(cls):
+    # pylint: disable=import-error,no-member
     import js  # Get pyodide object.
     external_input = CarefulReader(sys.stdin.buffer)
     external_output_method = lambda data: js.sendFromSandbox(data)
@@ -146,7 +147,7 @@ class Sandbox(object):
         ret = self._functions[fname](*args)
         self._send_to_js(Sandbox.DATA, ret)
       except Exception as e:
-        traceback.print_exc()
+        log.warn("Call error in %s: %s", fname, traceback.format_exc())
         self._send_to_js(Sandbox.EXC, "%s %s" % (type(e).__name__, e))
     if break_on_response:
       raise Exception("Sandbox disconnected unexpectedly")
diff --git a/sandbox/grist/summary.py b/sandbox/grist/summary.py
index d46d97d6..9df76a7f 100644
--- a/sandbox/grist/summary.py
+++ b/sandbox/grist/summary.py
@@ -1,13 +1,13 @@
 from collections import namedtuple
 import json
+import logging
 
 import six
 
 from column import is_visible_column
 import sort_specs
 
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 ColInfo = namedtuple('ColInfo', ('colId', 'type', 'isFormula', 'formula',
                                  'widgetOptions', 'label'))
@@ -134,7 +134,7 @@ def _update_sort_spec(sort_spec, old_table, new_table):
     new_sort_spec = [col_spec for col_spec in new_sort_spec if sort_specs.col_ref(col_spec)]
     return json.dumps(new_sort_spec, separators=(',', ':'))
   except Exception:
-    log.warn("update_summary_section: can't parse sortColRefs JSON; clearing sortColRefs")
+    log.warning("update_summary_section: can't parse sortColRefs JSON; clearing sortColRefs")
     return ''
 
 
diff --git a/sandbox/grist/table.py b/sandbox/grist/table.py
index 060625ac..9b976403 100644
--- a/sandbox/grist/table.py
+++ b/sandbox/grist/table.py
@@ -1,5 +1,6 @@
 import collections
 import itertools
+import logging
 import types
 
 import six
@@ -9,13 +10,12 @@ import column
 import depend
 import docmodel
 import functions
-import logger
 import lookup
 from records import adjust_record, Record as BaseRecord, RecordSet as BaseRecordSet
 import relation as relation_module    # "relation" is used too much as a variable name below.
 import usertypes
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 def get_default_func_name(col_id):
diff --git a/sandbox/grist/table_data_set.py b/sandbox/grist/table_data_set.py
index 18a79f12..b44b3701 100644
--- a/sandbox/grist/table_data_set.py
+++ b/sandbox/grist/table_data_set.py
@@ -1,11 +1,11 @@
+import logging
 from six.moves import zip as izip
 import six
 
 import actions
 from usertypes import get_type_default
 
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TableDataSet(object):
   """
@@ -32,7 +32,7 @@ class TableDataSet(object):
     try:
       getattr(self, action.__class__.__name__)(*action)
     except Exception as e:
-      log.warn("ERROR applying action %s: %s" % (action, e))
+      log.warning("ERROR applying action %s: %s", action, e)
       raise
 
   def apply_doc_actions(self, doc_actions):
diff --git a/sandbox/grist/test_column_actions.py b/sandbox/grist/test_column_actions.py
index 3416a095..b69b48e9 100644
--- a/sandbox/grist/test_column_actions.py
+++ b/sandbox/grist/test_column_actions.py
@@ -1,10 +1,10 @@
-import logger
+import logging
 
 import testutil
 import test_engine
 from test_engine import Table, Column, View, Section, Field
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestColumnActions(test_engine.EngineTestCase):
   sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/test_default_formulas.py b/sandbox/grist/test_default_formulas.py
index 497a2340..ff401e52 100644
--- a/sandbox/grist/test_default_formulas.py
+++ b/sandbox/grist/test_default_formulas.py
@@ -1,9 +1,9 @@
 import time
-import logger
+import logging
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestDefaultFormulas(test_engine.EngineTestCase):
   sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/test_derived.py b/sandbox/grist/test_derived.py
index bc367e09..a18f7d86 100644
--- a/sandbox/grist/test_derived.py
+++ b/sandbox/grist/test_derived.py
@@ -1,10 +1,10 @@
+import logging
 import actions
-import logger
 
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 def _bulk_update(table_name, col_names, row_data):
   return actions.BulkUpdateRecord(
diff --git a/sandbox/grist/test_display_cols.py b/sandbox/grist/test_display_cols.py
index ff54dfa5..7729e042 100644
--- a/sandbox/grist/test_display_cols.py
+++ b/sandbox/grist/test_display_cols.py
@@ -1,10 +1,10 @@
-import logger
+import logging
 
 import testutil
 import test_engine
 from test_engine import Table, Column
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestUserActions(test_engine.EngineTestCase):
   ref_sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/test_docmodel.py b/sandbox/grist/test_docmodel.py
index 6d273211..4f78598c 100644
--- a/sandbox/grist/test_docmodel.py
+++ b/sandbox/grist/test_docmodel.py
@@ -1,11 +1,11 @@
+import logging
 import actions
-import logger
 
 import testsamples
 import test_engine
 from test_engine import Table, Column
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestDocModel(test_engine.EngineTestCase):
 
diff --git a/sandbox/grist/test_engine.py b/sandbox/grist/test_engine.py
index 357e3c9d..435fa177 100644
--- a/sandbox/grist/test_engine.py
+++ b/sandbox/grist/test_engine.py
@@ -1,6 +1,7 @@
 import difflib
 import functools
 import json
+import logging
 import unittest
 from collections import namedtuple
 from pprint import pprint
@@ -10,12 +11,11 @@ import six
 import actions
 import column
 import engine
-import logger
 import useractions
 import testutil
 import objtypes
 
-log = logger.Logger(__name__, logger.DEBUG)
+log = logging.getLogger(__name__)
 
 # These are for use in verifying metadata using assertTables/assertViews methods. E.g.
 #   self.assertViews([View(1, sections=[Section(1, parentKey="record", tableRef=1, fields=[
@@ -35,17 +35,14 @@ class EngineTestCase(unittest.TestCase):
   Provides functionality for verifying engine actions and data, which is general enough to be
   useful for other tests. It is also used by TestEngine below.
   """
-  # Place to keep the original log handler (which we modify for the duration of the test).
-  # We can't use cls._orig_log_handler directly because then Python it's an actual class method.
-  _orig_log_handler = []
-
   @classmethod
   def setUpClass(cls):
-    cls._orig_log_handler.append(logger.set_handler(testutil.limit_log_stderr(logger.WARN)))
+    cls._orig_log_level = logging.root.level
+    logging.root.setLevel(logging.WARNING)
 
   @classmethod
   def tearDownClass(cls):
-    logger.set_handler(cls._orig_log_handler.pop())
+    logging.root.setLevel(cls._orig_log_level)
 
 
   def setUp(self):
@@ -247,7 +244,10 @@ class EngineTestCase(unittest.TestCase):
     if sort:
       row_ids.sort(key=lambda r: sort(table.get_record(r)))
 
-    observed_col_data = {c.col_id: [c.raw_get(r) for r in row_ids] for c in columns if c.col_id != "id"}
+    observed_col_data = {
+      c.col_id: [c.raw_get(r) for r in row_ids]
+      for c in columns if c.col_id != "id"
+    }
     observed = actions.TableData(table_name, row_ids, observed_col_data)
     self.assertEqualDocData({table_name: observed}, {table_name: expected},
                             col_names=col_names)
@@ -353,7 +353,7 @@ class EngineTestCase(unittest.TestCase):
 
   def apply_user_action(self, user_action_repr, is_undo=False, user=None):
     if not is_undo:
-      log.debug("Applying user action %r" % (user_action_repr,))
+      log.debug("Applying user action %r", user_action_repr)
       if self._undo_state_tracker is not None:
         doc_state = self.getFullEngineData()
 
@@ -384,7 +384,7 @@ def test_undo(test_method):
     self._undo_state_tracker = []
     test_method(self)
     for (expected_engine_data, undo_actions) in reversed(self._undo_state_tracker):
-      log.debug("Applying undo actions %r" % (undo_actions,))
+      log.debug("Applying undo actions %r", undo_actions)
       self.apply_undo_actions(undo_actions)
       self.assertEqualDocData(self.getFullEngineData(), expected_engine_data)
   return wrapped
diff --git a/sandbox/grist/test_import_actions.py b/sandbox/grist/test_import_actions.py
index 2da27ba1..c7e919ed 100644
--- a/sandbox/grist/test_import_actions.py
+++ b/sandbox/grist/test_import_actions.py
@@ -1,8 +1,8 @@
 # pylint: disable=line-too-long
-import logger
+import logging
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class TestImportActions(test_engine.EngineTestCase):
diff --git a/sandbox/grist/test_logger.py b/sandbox/grist/test_logger.py
deleted file mode 100644
index 07f5f4e5..00000000
--- a/sandbox/grist/test_logger.py
+++ /dev/null
@@ -1,38 +0,0 @@
-import unittest
-import logger
-
-
-class TestLogger(unittest.TestCase):
-  def _log_handler(self, level, name, msg):
-    self.messages.append((level, name, msg))
-
-  def setUp(self):
-    self.messages = []
-    self.orig_handler = logger.set_handler(self._log_handler)
-
-  def tearDown(self):
-    logger.set_handler(self.orig_handler)
-
-  def test_logger(self):
-    log = logger.Logger("foo", logger.INFO)
-    log.info("Hello Info")
-    log.debug("Hello Debug")
-    log.warn("Hello Warn")
-
-    self.assertEqual(self.messages, [
-      (logger.INFO, 'foo', 'Hello Info'),
-      (logger.WARN, 'foo', 'Hello Warn'),
-    ])
-    del self.messages[:]
-
-    log = logger.Logger("baz", logger.DEBUG)
-    log.debug("Hello Debug")
-    log.info("Hello Info")
-    self.assertEqual(self.messages, [
-      (logger.DEBUG, 'baz', 'Hello Debug'),
-      (logger.INFO, 'baz', 'Hello Info'),
-    ])
-
-
-if __name__ == "__main__":
-  unittest.main()
diff --git a/sandbox/grist/test_lookups.py b/sandbox/grist/test_lookups.py
index a9281319..9b69c72a 100644
--- a/sandbox/grist/test_lookups.py
+++ b/sandbox/grist/test_lookups.py
@@ -1,11 +1,11 @@
+import logging
 import actions
-import logger
 
 import testsamples
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 def _bulk_update(table_name, col_names, row_data):
   return actions.BulkUpdateRecord(
diff --git a/sandbox/grist/test_record_func.py b/sandbox/grist/test_record_func.py
index 520b2046..e0252949 100644
--- a/sandbox/grist/test_record_func.py
+++ b/sandbox/grist/test_record_func.py
@@ -1,15 +1,16 @@
+# pylint: disable=line-too-long
 import datetime
+import logging
 import actions
-import logger
 import moment
 import objtypes
+from objtypes import RecordStub
 
 import testsamples
 import testutil
 import test_engine
-from objtypes import RecordStub
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 def _bulk_update(table_name, col_names, row_data):
   return actions.BulkUpdateRecord(
diff --git a/sandbox/grist/test_reflist_rel.py b/sandbox/grist/test_reflist_rel.py
index 1e3e7615..59f24aa8 100644
--- a/sandbox/grist/test_reflist_rel.py
+++ b/sandbox/grist/test_reflist_rel.py
@@ -2,11 +2,11 @@
 This test replicates a bug involving a column conversion after a table rename in the presence of
 a RefList. A RefList column type today only appears as a result of detaching a summary table.
 """
-import logger
+import logging
 import test_engine
 from test_engine import Table, Column
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestRefListRelation(test_engine.EngineTestCase):
   def test_ref_list_relation(self):
diff --git a/sandbox/grist/test_relabeling.py b/sandbox/grist/test_relabeling.py
index ef55b992..4f3159d3 100644
--- a/sandbox/grist/test_relabeling.py
+++ b/sandbox/grist/test_relabeling.py
@@ -1,11 +1,10 @@
+import unittest
+import sys
 import relabeling
 
 from sortedcontainers import SortedListWithKey
 from six.moves import zip as izip, xrange
 
-import unittest
-import sys
-
 # Shortcut to keep code more concise.
 r = relabeling
 
diff --git a/sandbox/grist/test_renames.py b/sandbox/grist/test_renames.py
index 51c1f990..5fac8f31 100644
--- a/sandbox/grist/test_renames.py
+++ b/sandbox/grist/test_renames.py
@@ -1,10 +1,10 @@
 # -*- coding: utf-8 -*-
-import logger
+import logging
 
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class TestRenames(test_engine.EngineTestCase):
diff --git a/sandbox/grist/test_renames2.py b/sandbox/grist/test_renames2.py
index ce0ed111..851470c7 100644
--- a/sandbox/grist/test_renames2.py
+++ b/sandbox/grist/test_renames2.py
@@ -1,11 +1,11 @@
 import textwrap
 import unittest
 
-import logger
+import logging
 import six
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 def _replace_col_name(data, old_name, new_name):
diff --git a/sandbox/grist/test_summary.py b/sandbox/grist/test_summary.py
index 0dc1ee67..fa19df8a 100644
--- a/sandbox/grist/test_summary.py
+++ b/sandbox/grist/test_summary.py
@@ -3,16 +3,15 @@ Test of Summary tables. This has many test cases, so to keep files smaller, it's
 files: test_summary.py and test_summary2.py.
 """
 
+import logging
 import actions
-import logger
 import summary
 import testutil
 import test_engine
+from test_engine import Table, Column, View, Section, Field
 from useractions import allowed_summary_change
 
-from test_engine import Table, Column, View, Section, Field
-
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class TestSummary(test_engine.EngineTestCase):
diff --git a/sandbox/grist/test_summary2.py b/sandbox/grist/test_summary2.py
index 7f21c397..0a9fae20 100644
--- a/sandbox/grist/test_summary2.py
+++ b/sandbox/grist/test_summary2.py
@@ -1,16 +1,16 @@
+# pylint:disable=too-many-lines
 """
 Test of Summary tables. This has many test cases, so to keep files smaller, it's split into two
 files: test_summary.py and test_summary2.py.
 """
+import logging
 import actions
-import logger
 import test_engine
+from test_engine import Table, Column, View, Section, Field
 import test_summary
 import testutil
 
-from test_engine import Table, Column, View, Section, Field
-
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class TestSummary2(test_engine.EngineTestCase):
diff --git a/sandbox/grist/test_summary_choicelist.py b/sandbox/grist/test_summary_choicelist.py
index be0171da..3ac96dbb 100644
--- a/sandbox/grist/test_summary_choicelist.py
+++ b/sandbox/grist/test_summary_choicelist.py
@@ -1,13 +1,14 @@
+# pylint: disable=line-too-long
 """
 Test of Summary tables grouped by ChoiceList columns.
 """
+import logging
 import column
-import logger
 import lookup
 import testutil
 from test_engine import EngineTestCase, Table, Column, test_undo
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 class TestSummaryChoiceList(EngineTestCase):
diff --git a/sandbox/grist/test_summary_undo.py b/sandbox/grist/test_summary_undo.py
index 93499df7..a25d68c1 100644
--- a/sandbox/grist/test_summary_undo.py
+++ b/sandbox/grist/test_summary_undo.py
@@ -1,11 +1,11 @@
 """
 Some more test cases for summary tables, involving UNDO.
 """
-import logger
+import logging
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestSummaryUndo(test_engine.EngineTestCase):
   sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/test_table_actions.py b/sandbox/grist/test_table_actions.py
index f6576cf0..3ae896ec 100644
--- a/sandbox/grist/test_table_actions.py
+++ b/sandbox/grist/test_table_actions.py
@@ -1,10 +1,10 @@
-import logger
+import logging
 
 import testutil
 import test_engine
 from test_engine import Table, Column, View, Section, Field
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestTableActions(test_engine.EngineTestCase):
 
diff --git a/sandbox/grist/test_trigger_formulas.py b/sandbox/grist/test_trigger_formulas.py
index 1ea512f7..e1574357 100644
--- a/sandbox/grist/test_trigger_formulas.py
+++ b/sandbox/grist/test_trigger_formulas.py
@@ -1,9 +1,9 @@
 import copy
+import logging
 import time
 
 import six
 
-import logger
 import objtypes
 import testutil
 import test_engine
@@ -11,7 +11,7 @@ from schema import RecalcWhen
 
 # pylint: disable=line-too-long
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 def column_error(table, column, user_input):
   return objtypes.RaisedException(
diff --git a/sandbox/grist/test_types.py b/sandbox/grist/test_types.py
index a505d87c..c665438a 100644
--- a/sandbox/grist/test_types.py
+++ b/sandbox/grist/test_types.py
@@ -1,12 +1,12 @@
 # -*- coding: utf-8 -*-
 # pylint: disable=line-too-long
+import logging
 import six
 
-import logger
 import testutil
 import test_engine
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestTypes(test_engine.EngineTestCase):
   sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/test_useractions.py b/sandbox/grist/test_useractions.py
index 489b7eae..5fd54f41 100644
--- a/sandbox/grist/test_useractions.py
+++ b/sandbox/grist/test_useractions.py
@@ -1,6 +1,7 @@
+# pylint:disable=too-many-lines
 import json
 import types
-import logger
+import logging
 import useractions
 
 import testutil
@@ -8,7 +9,7 @@ import test_engine
 from test_engine import Table, Column, View, Section, Field
 from schema import RecalcWhen
 
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 class TestUserActions(test_engine.EngineTestCase):
   sample = testutil.parse_test_sample({
diff --git a/sandbox/grist/testutil.py b/sandbox/grist/testutil.py
index e0f104d1..8ae899c6 100644
--- a/sandbox/grist/testutil.py
+++ b/sandbox/grist/testutil.py
@@ -6,18 +6,6 @@ import re
 import six
 
 import actions
-import logger
-
-def limit_log_stderr(min_level):
-  """
-  Returns a log handler suitable for logger.set_handler(), which logs using log_stderr but only
-  messages at the given level or higher.
-  """
-  def handler(level, name, msg):
-    if level >= min_level:
-      logger.log_stderr(level, name, msg)
-  return handler
-
 
 def table_data_from_rows(table_id, col_names, rows):
   """
diff --git a/sandbox/grist/useractions.py b/sandbox/grist/useractions.py
index 5d8d0c8c..d0b43792 100644
--- a/sandbox/grist/useractions.py
+++ b/sandbox/grist/useractions.py
@@ -2,6 +2,7 @@
 from collections import namedtuple, Counter, OrderedDict
 import re
 import json
+import logging
 import sys
 from contextlib import contextmanager
 
@@ -27,8 +28,7 @@ import treeview
 
 from table import get_validation_func_name
 
-import logger
-log = logger.Logger(__name__, logger.INFO)
+log = logging.getLogger(__name__)
 
 
 _current_module = sys.modules[__name__]
diff --git a/sandbox/grist/usertypes.py b/sandbox/grist/usertypes.py
index 64c17fd5..28f60a56 100644
--- a/sandbox/grist/usertypes.py
+++ b/sandbox/grist/usertypes.py
@@ -15,6 +15,7 @@ the extra complexity.
 import csv
 import datetime
 import json
+import logging
 import math
 
 import six
@@ -22,9 +23,9 @@ from six import integer_types
 import objtypes
 from objtypes import AltText, is_int_short
 import moment
-import logger
 from records import Record, RecordSet
-log = logger.Logger(__name__, logger.INFO)
+
+log = logging.getLogger(__name__)
 
 NoneType = type(None)