added null machine to standard lib

src/pygcode/__init__.py

@@ -24,7 +24,10 @@ __copyright__ = "Copyright (c) 2017 {0}".format(__author__)
 # =========================== Imports ===========================
 __all__ = [
     # Machine
-    'Machine', 'Position', 'CoordinateSystem', 'State', 'Mode',
+    'Machine', 'State', 'Mode',
+    'NullMachine', 'NullState', 'NullMode',
+    'Position', 'CoordinateSystem',
+
     # Line
     'Line',
     # Block
@@ -165,8 +168,8 @@ __all__ = [
 # Machine
 from .machine import (
     Position, CoordinateSystem,
-    State, Mode,
-    Machine,
+    Machine, State, Mode,
+    NullMachine, NullState, NullMode,
 )
 
 # Line

src/pygcode/machine.py

@@ -503,3 +503,16 @@ class Machine(object):
             new_pos = self.pos
             new_pos.update(**coords)  # only change given coordinates
             self.pos = new_pos
+
+
+# Null Machine
+#   A machine that presumes nothing
+class NullMode(Mode):
+    default_mode = ''
+
+class NullState(State):
+    pass  # no change (yet)
+
+class NullMachine(Machine):
+    MODE_CLASS = NullMode
+    STATE_CLASS = NullState