Refactor code to access values from task_vars

roles/openshift_health_checker/openshift_checks/__init__.py

@@ -5,8 +5,10 @@ Health checks for OpenShift clusters.
 import os
 from abc import ABCMeta, abstractmethod, abstractproperty
 from importlib import import_module
+import operator
 
 import six
+from six.moves import reduce
 
 
 class OpenShiftCheckException(Exception):
@@ -54,6 +56,22 @@ class OpenShiftCheck(object):
                 yield subclass
 
 
+def get_var(task_vars, *keys, **kwargs):
+    """Helper function to get deeply nested values from task_vars.
+
+    Ansible task_vars structures are Python dicts, often mapping strings to
+    other dicts. This helper makes it easier to get a nested value, raising
+    OpenShiftCheckException when a key is not found.
+    """
+    try:
+        value = reduce(operator.getitem, keys, task_vars)
+    except (KeyError, TypeError):
+        if "default" in kwargs:
+            return kwargs["default"]
+        raise OpenShiftCheckException("'{}' is undefined".format(".".join(map(str, keys))))
+    return value
+
+
 # Dynamically import all submodules for the side effect of loading checks.
 
 EXCLUDES = (

roles/openshift_health_checker/openshift_checks/mixins.py

@@ -1,5 +1,5 @@
 # pylint: disable=missing-docstring
-from openshift_checks import OpenShiftCheckException
+from openshift_checks import get_var
 
 
 class NotContainerized(object):
@@ -18,7 +18,4 @@ class NotContainerized(object):
 
     @staticmethod
     def is_containerized(task_vars):
-        try:
-            return task_vars["openshift"]["common"]["is_containerized"]
-        except (KeyError, TypeError):
-            raise OpenShiftCheckException("'openshift.common.is_containerized' is undefined")
+        return get_var(task_vars, "openshift", "common", "is_containerized")

roles/openshift_health_checker/openshift_checks/package_availability.py

@@ -1,5 +1,5 @@
 # pylint: disable=missing-docstring
-from openshift_checks import OpenShiftCheck, OpenShiftCheckException
+from openshift_checks import OpenShiftCheck, get_var
 from openshift_checks.mixins import NotContainerized
 
 
@@ -10,12 +10,8 @@ class PackageAvailability(NotContainerized, OpenShiftCheck):
     tags = ["preflight"]
 
     def run(self, tmp, task_vars):
-        try:
-            rpm_prefix = task_vars["openshift"]["common"]["service_type"]
-        except (KeyError, TypeError):
-            raise OpenShiftCheckException("'openshift.common.service_type' is undefined")
-
-        group_names = task_vars.get("group_names", [])
+        rpm_prefix = get_var(task_vars, "openshift", "common", "service_type")
+        group_names = get_var(task_vars, "group_names", default=[])
 
         packages = set()
 

roles/openshift_health_checker/openshift_checks/package_version.py

@@ -1,5 +1,5 @@
 # pylint: disable=missing-docstring
-from openshift_checks import OpenShiftCheck, OpenShiftCheckException
+from openshift_checks import OpenShiftCheck, get_var
 from openshift_checks.mixins import NotContainerized
 
 
@@ -17,10 +17,7 @@ class PackageVersion(NotContainerized, OpenShiftCheck):
         )
 
     def run(self, tmp, task_vars):
-        try:
-            openshift_release = task_vars["openshift_release"]
-        except (KeyError, TypeError):
-            raise OpenShiftCheckException("'openshift_release' is undefined")
+        openshift_release = get_var(task_vars, "openshift_release")
 
         args = {"version": openshift_release}
         return self.module_executor("aos_version", args, tmp, task_vars)