refactor to allow use with console entry points

cellxgene_gateway/env.py

@@ -0,0 +1,46 @@
+# Copyright 2019 Novartis Institutes for BioMedical Research Inc. 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.
+
+import os
+
+deployment_env = os.environ.get("DEPLOYMENT_ENV")
+cellxgene_location = os.environ.get("CELLXGENE_LOCATION")
+cellxgene_data = os.environ.get("CELLXGENE_DATA")
+gateway_host = os.environ.get("GATEWAY_HOST")
+gateway_protocol = os.environ.get("GATEWAY_PROTOCOL")
+ip = os.environ.get("GATEWAY_IP")
+
+env_vars = {
+    "DEPLOYMENT_ENV": deployment_env,
+    "CELLXGENE_LOCATION": cellxgene_location,
+    "CELLXGENE_DATA": cellxgene_data,
+    "GATEWAY_HOST": gateway_host,
+    "GATEWAY_PROTOCOL": gateway_protocol,
+    "GATEWAY_IP": ip,
+}
+
+if not all(env_vars.values()):
+    raise ValueError(
+        f"""
+Please ensure that environment variables are set correctly.
+The ones with None below are missing and need to be set.
+
+{env_vars}
+
+Set them at the terminal before running the gateway.
+An example is:
+
+    export CELLXGENE_LOCATION=~/anaconda/envs/cellxgene-dev/bin/cellxgene
+    export CELLXGENE_DATA=../cellxgene_data
+    export DEPLOYMENT_ENV=dev
+    export GATEWAY_HOST=localhost:5005
+    export GATEWAY_PROTOCOL=http
+    export GATEWAY_IP=127.0.0.1
+"""
+    )