Add default position, deflection, and step to AFMPiezo.move_to_pos_or_def.

diff --git a/pypiezo/afm.py b/pypiezo/afm.py
index 616c6f4b6c3d039bf9b916ab961bca1a4dda6d6d..bfc9585e9a6edbc5c8a5fb208e7de2e318a8e5e1 100644 (file)
--- a/pypiezo/afm.py
+++ b/pypiezo/afm.py
@@ -167,14 +167,17 @@ class AFMPiezo (_base.Piezo):
         "Return a Numpy dtype suitable for deflection bit values."
         return self._deflection_channel().subdevice.get_dtype()
 
-    def move_to_pos_or_def(self, axis_name, position, deflection, step,
-                           return_data=False, pre_move_steps=0):
+    def move_to_pos_or_def(self, axis_name, position=None, deflection=None,
+                           step=1, return_data=False, pre_move_steps=0):
         """TODO
 
         pre_move_steps : int
             number of 'null' steps to take before moving (confirming a
             stable input deflection).
         """
+        if position is None and deflection is None:
+            raise ValueError('must specify position, deflection, or both')
+
         if return_data or _package_config['matplotlib']:
             aquire_data = True
         else:
@@ -187,6 +190,18 @@ class AFMPiezo (_base.Piezo):
         elif step > 0 and position < self.last_output[axis_name]:
             step = -step
 
+        if position is None:
+            # default to the extreme value in the step direction
+            if step > 0:
+                axis = self.axis_by_name(axis_name)
+                position = axis.channel.get_maxdata()
+            else:
+                position = 0
+        elif deflection is None:
+            # default to the extreme value
+            channel = self._deflection_channel(self)
+            deflection = channel.get_maxdata()
+
         log_string = (
             'move to position %d or deflection %g on axis %s in steps of %d'
             % (position, deflection, axis_name, step))