refactor: simplify registry reads with setuphelpers

setup.py

@@ -11,20 +11,37 @@ import os
 
 uninstallkey = []
 
+# Relative subdirectories under ProgramData used for this package's rollback state.
 STATE_DIRECTORY = ('Comitari', 'HardeningSafe')
+# Stores original registry values plus their package target for conditional rollback.
 STATE_FILENAME = 'original-values.json'
 
 # Intentionally limited machine-wide controls. Keep state-file paths in the
 # legacy PowerShell format so existing installations can roll back safely.
+#
+# SETTINGS entry parameters:
+#   Path  - HKLM registry key in the format accepted by _registry_path().
+#           These keys apply to the computer, rather than one signed-in user.
+#   Name  - exact Windows policy value name within that key.
+#   Value - desired integer REG_DWORD written by _write_value().
 SETTINGS = (
+    # Set the machine policy that disables AutoRun commands.
     {'Path': r'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer',
      'Name': 'NoAutorun', 'Value': 1},
+
+    # Disable AutoPlay for every drive type (0xFF mask).
     {'Path': r'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer',
      'Name': 'NoDriveTypeAutoRun', 'Value': 255},
+
+    # Disable AutoPlay for devices that do not expose a volume.
     {'Path': r'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Explorer',
      'Name': 'NoAutoplayfornonVolume', 'Value': 1},
+
+    # Prevent use of the camera from the Windows lock screen.
     {'Path': r'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Personalization',
      'Name': 'NoLockScreenCamera', 'Value': 1},
+
+    # Prevent enabling a slideshow on the Windows lock screen.
     {'Path': r'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Personalization',
      'Name': 'NoLockScreenSlideshow', 'Value': 1},
 )
@@ -46,10 +63,11 @@ def _read_value(path, name):
     subkey = _registry_path(path)
     if not reg_key_exists(HKEY_LOCAL_MACHINE, subkey):
         return {'Exists': False, 'Value': None}
-    if not reg_value_exists(HKEY_LOCAL_MACHINE, subkey, name):
-        return {'Exists': False, 'Value': None}
+    missing = object()
     with reg_openkey_noredir(HKEY_LOCAL_MACHINE, subkey) as key:
-        value = reg_getvalue(key, name)
+        value = reg_getvalue(key, name, default=missing)
+    if value is missing:
+        return {'Exists': False, 'Value': None}
     if value is None:
         raise RuntimeError('Registry value disappeared while it was being read: %s' % name)
     try: