lense -> nmget

scripts/update-policy.py

@@ -1,6 +1,7 @@
 from collections import OrderedDict
 from collections.abc import Mapping
 from itertools import chain
+from typing import Any, Mapping
 
 import oyaml
 import requests
@@ -24,25 +25,53 @@ def increase_indent(self, flow=False, indentless=False):
         return super(OYAMLDumper, self).increase_indent(flow, False)
 
 
-def lense(obj, *args):
-    if len(args) == 0 and obj is not None:
-        return obj
-
-    if not isinstance(obj, Mapping):
-        return None
-
-    return lense(obj.get(args[0], None), *args[1:])
+def nmget(
+    o: Mapping[str, Any],
+    key_path: str,
+    def_val: Any = None,
+    path_delimiter: str = ".",
+    null_as_default: bool = True,
+) -> Any:
+    """
+    A short-hand for retrieving a value from nested mappings
+    ("nested-mapping-get"). At each level it checks if the given "path"
+    component in the given key exists and return the default value whenever
+    fails.
+    Example:
+    >>> o = {'a':{'b':1}, 'x': None}
+    >>> nmget(o, 'a', 0)
+    {'b': 1}
+    >>> nmget(o, 'a.b', 0)
+    1
+    >>> nmget(o, 'a/b', 0, '/')
+    1
+    >>> nmget(o, 'a.c', 0)
+    0
+    >>> nmget(o, 'x', 0)
+    0
+    >>> nmget(o, 'x', 0, null_as_default=False)
+    None
+    """
+    pieces = key_path.split(path_delimiter)
+    while pieces:
+        p = pieces.pop(0)
+        if o is None or p not in o:
+            return def_val
+        o = o[p]
+    if o is None and null_as_default:
+        return def_val
+    return o
 
 
 def filter_syscalls(processor_arch, syscalls_item):
     if syscalls_item["action"] != "SCMP_ACT_ALLOW":
         return []
 
-    excludes = lense(syscalls_item, "excludes", "arches")
+    excludes = nmget(syscalls_item, "excludes.arches")
     if excludes and processor_arch in excludes:
         return []
 
-    includes = lense(syscalls_item, "includes", "arches")
+    includes = nmget(syscalls_item, "includes.arches")
     if includes and not processor_arch in includes:
         return []