Fail printers_available on unrecognized sys.platform

Author: pjkundert

slip39/gui/main.py

@@ -1102,7 +1102,7 @@ def app(
             # A -SAVE- target directory has been selected; use it, if possible.  This is where any
             # output will be written.  It should usually be a removable volume, but we do not check.
             # An empty path implies the current directory.
-            filepath		= None
+            filepath,printer	= None,None
             if event == '-SAVE-':
                 filepath	= values['-SAVE-']
                 log.info( f"Saving to {filepath!r}..." )

slip39/layout/__init__.py

@@ -934,7 +934,7 @@ def printers_available():
         command		= [ '/usr/bin/lpstat', '-lt' ]
         command_input	= None
     else:
-        return
+        raise NotImplementedError( f"Printing not supported on platform {sys.platform}" )
 
     subproc			= subprocess.run(
         command,