title: pass environment variables in iot edge module
body: <p>I am building a Microsoft IoT edge python module for my Linux arm device. I have to access the environment variables in the python module from my deployment.template.json file. The file shows how the environment variables are passed from the environment to the module. The problem is how to access them inside the code. </p>
  
  <p><strong><em>deployment.template.json file:</em></strong></p>
  
  <pre><code>  "$schema-template": "2.0.0",
    "modulesContent": {
      "$edgeAgent": {
        "properties.desired": {
          "schemaVersion": "1.0",
          "runtime": {
            "type": "docker",
            "settings": {
              "minDockerVersion": "v1.25",
              "loggingOptions": "",
              "registryCredentials": {
                "myRegistryName": {
                  "username": "$CONTAINER_REGISTRY_USERNAME",
                  "password": "$CONTAINER_REGISTRY_PASSWORD",
                  "address": "myRegistryAddress.azurecr.io"
                }
              }
            }
          },
          "systemModules": {
            "edgeAgent": {
              "type": "docker",
              "settings": {
                "image": "mcr.microsoft.com/azureiotedge-agent:1.0",
                "createOptions": {}
              }
            },
            "edgeHub": {
              "type": "docker",
              "status": "running",
              "restartPolicy": "always",
              "settings": {
                "image": "mcr.microsoft.com/azureiotedge-hub:1.0",
                "createOptions": {
                  "HostConfig": {
                    "PortBindings": {
                      "5671/tcp": [
                        {
                          "HostPort": "5671"
                        }
                      ],
                      "8883/tcp": [
                        {
                          "HostPort": "8883"
                        }
                      ],
                      "443/tcp": [
                        {
                          "HostPort": "443"
                        }
                      ]
                    }
                  }
                }
              }
            }
          },
          "modules": {
            "Module_Name": {
              "version": "1.0",
              "type": "docker",
              "status": "running",
              "restartPolicy": "always",
              "settings": {
                "image": "${MODULES.Module_Name}",
                "createOptions": {}
              },
              "env": {
                "test_var": {
                  "value": "secret"
                }
              }
            }
          }
        }
      },
      "$edgeHub": {
        "properties.desired": {
          "schemaVersion": "1.0",
          "routes": {
            "route": "FROM /messages/* INTO $upstream"
          },
          "storeAndForwardConfiguration": {
            "timeToLiveSecs": 7200
          }
        }
      }
    }
  }
  </code></pre>
  
  <p>How can I access the environment <code>test_var</code> variable inside the python code module?</p>