From 7eeeb24087419575a3b38e95769f5f4f7cd38514 Mon Sep 17 00:00:00 2001
From: Acme Contributor <noreply@google.com>
Date: Mon, 17 Aug 2020 07:11:14 -0700
Subject: [PATCH] Add constant info logger.

PiperOrigin-RevId: 327014404
Change-Id: I84884cc9019064d2bb2be8556d4c794d78e14f34
---
 acme/utils/loggers/__init__.py |  1 +
 acme/utils/loggers/constant.py | 44 ++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 acme/utils/loggers/constant.py

diff --git a/acme/utils/loggers/__init__.py b/acme/utils/loggers/__init__.py
index da162bb686..e0f5792bd1 100644
--- a/acme/utils/loggers/__init__.py
+++ b/acme/utils/loggers/__init__.py
@@ -21,6 +21,7 @@
 from acme.utils.loggers.base import LoggingData
 from acme.utils.loggers.base import NoOpLogger
 from acme.utils.loggers.base import to_numpy
+from acme.utils.loggers.constant import ConstantLogger
 from acme.utils.loggers.csv import CSVLogger
 from acme.utils.loggers.filters import NoneFilter
 from acme.utils.loggers.filters import TimeFilter
diff --git a/acme/utils/loggers/constant.py b/acme/utils/loggers/constant.py
new file mode 100644
index 0000000000..dafd98c752
--- /dev/null
+++ b/acme/utils/loggers/constant.py
@@ -0,0 +1,44 @@
+# Lint as: python3
+# Copyright 2018 DeepMind Technologies Limited. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Acme specific utils."""
+from acme.utils.loggers import base
+
+
+class ConstantLogger(base.Logger):
+  """Logger for values that remain constant throughout the experiment.
+
+  This logger is used to log additional values e.g. level_name or
+  hyperparameters that do not change in an experiment. Having these values
+  allows to group or facet plots when analysing data post-experiment.
+  """
+
+  def __init__(self,
+               constant_data: base.LoggingData,
+               to: base.Logger):
+    """Initialise the extra info logger.
+
+    Args:
+      constant_data: Dictionary containing the constant info to be logged.
+      to: The logger to add these extra info to.
+    """
+    self._constant_data = constant_data
+    self._to = to
+
+  def write(self, data: base.LoggingData):
+    # Need to create a new mutable dictionary that will be updated with the data
+    # we will be writing. base.LoggingData is immutable and hence cannot be
+    # updated.
+    self._to.write({**self._constant_data, **data})