adds voila env variable example

Author: edublancas

examples/voila/env-variable/app.ipynb

@@ -0,0 +1,58 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "83a15137-3ea2-47d4-871a-382213ba046e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from os import environ\n",
+    "\n",
+    "value = environ.get(\"ENV_VAR\", None)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "764d3d46-11fb-4689-bf2f-a8558205323f",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "ENV_VAR is undefined\n"
+     ]
+    }
+   ],
+   "source": [
+    "if value is None:\n",
+    "    print(\"ENV_VAR is undefined\")\n",
+    "else:\n",
+    "    print(f\"EN_VAR: {value}\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.11.5"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}