Add example_variables DAG

examples/intro-example/dags/config/example_variables.json

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+{
+	"example_variables_config": {
+		"var1": "value1",
+		"var2": [1, 2, 3],
+		"var3": {
+			"k": "value3"
+		}
+	}
+}

examples/intro-example/dags/example_variables.py

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+from __future__ import print_function
+
+from datetime import datetime
+
+from airflow import DAG
+from airflow.models import Variable
+from airflow.operators.dummy_operator import DummyOperator
+from airflow.operators.bash_operator import BashOperator
+
+default_args = {
+    'owner': 'airflow',
+    'start_date': datetime(2019, 2, 15),
+    'end_date': datetime(2019, 2, 15)    
+}
+
+dag = DAG('example_variables', 
+    schedule_interval="@once", 
+    default_args=default_args)
+
+
+# Config variables
+## Common
+# var1 = "value1"
+# var2 = [1, 2, 3]
+# var3 = {'k': 'value3'}
+
+## Better
+# var1 = Variable.get("var1")
+# var2 = Variable.get("var2")
+# var3 = Variable.get("var3")
+
+## Recommended way
+dag_config = Variable.get("example_variables_config", deserialize_json=True)
+var1 = dag_config["var1"]
+var2 = dag_config["var2"]
+var3 = dag_config["var3"]
+
+# print (type(var1))
+# print (type(var2))
+# print (type(var3))
+
+start = DummyOperator(
+    task_id="start",
+    dag=dag
+)
+
+# To test this task, run this command:
+# docker-compose run --rm webserver airflow test example_variables get_dag_config 2019-02-15
+t1 = BashOperator(
+    task_id="get_dag_config",
+    bash_command='echo "{0}"'.format(dag_config),
+    dag=dag,
+)
+
+# You can use a variable from a jinja template
+## {{ var.value.<variable_name> }}
+
+t2 = BashOperator(
+    task_id="get_variable_value",
+    bash_command='echo {{ var.value.var3 }} ',
+    dag=dag,
+)
+
+## {{ var.json.<variable_name> }}
+t3 = BashOperator(
+    task_id="get_variable_json",
+    bash_command='echo {{ var.json.example_variables_config.var3 }} ',
+    dag=dag,
+)
+
+start >> [t1, t2, t3]