[AIRFLOW-4207] Metaclass class argument for Python 3 (apache#5024)

airflow/contrib/kubernetes/kubernetes_request_factory/kubernetes_request_factory.py

@@ -19,13 +19,12 @@
 import six
 
 
-class KubernetesRequestFactory:
+class KubernetesRequestFactory(metaclass=ABCMeta):
     """
     Create requests to be sent to kube API.
     Extend this class to talk to kubernetes and generate your specific resources.
     This is equivalent of generating yaml files that can be used by `kubectl`
     """
-    __metaclass__ = ABCMeta
 
     @abstractmethod
     def create(self, pod):

airflow/dag/base_dag.py

@@ -20,11 +20,10 @@
 from abc import ABCMeta, abstractmethod
 
 
-class BaseDag():
+class BaseDag(metaclass=ABCMeta):
     """
     Base DAG object that both the SimpleDag and DAG inherit.
     """
-    __metaclass__ = ABCMeta
 
     @property
     @abstractmethod

airflow/models/baseoperator.py

@@ -979,13 +979,11 @@ def get_extra_links(self, dttm, link_name):
             return self.global_operator_extra_link_dict[link_name].get_link(self, dttm)
 
 
-class BaseOperatorLink:
+class BaseOperatorLink(metaclass=ABCMeta):
     """
     Abstract base class that defines how we get an operator link.
     """
 
-    __metaclass__ = ABCMeta
-
     @property
     @abstractmethod
     def name(self):

airflow/utils/dag_processing.py

@@ -366,11 +366,10 @@ def list_py_file_paths(directory, safe_mode=True,
     return file_paths
 
 
-class AbstractDagFileProcessor(object):
+class AbstractDagFileProcessor(metaclass=ABCMeta):
     """
     Processes a DAG file. See SchedulerJob.process_file() for more details.
     """
-    __metaclass__ = ABCMeta
 
     @abstractmethod
     def start(self):