frappy_psi.parmod: extract a tuple element as own moudle

Change-Id: I8d904ed21f8a5c16ae71daf30c9a1ea42876b451

frappy_psi/parmod.py

@@ -21,12 +21,12 @@
 
 """modules to access parameters"""
 
+import re
 from frappy.core import Drivable, EnumType, IDLE, Attached, StringType, Property, \
     Parameter, BoolType, FloatRange, Readable, ERROR, nopoll
 from frappy.errors import ConfigError
 from frappy_psi.convergence import HasConvergence
 from frappy_psi.mixins import HasRamp
-from frappy.lib import merge_status
 
 
 class Par(Readable):
@@ -255,3 +255,41 @@ class SwitchDriv(HasConvergence, Drivable):
         self.log.info('target=%g (%s)', target, this.name)
         this.write_target(target1)
         return target
+
+
+INDEX = re.compile(r'(.*)\[(.*)\]')
+
+
+class Comp(Readable):
+    value = Parameter(datatype=FloatRange(unit='$'))
+    read = Attached(description='<module>.<parameter> for read')
+    unit = Property('main unit', StringType())
+
+    _parname = None
+    _index = None
+
+    def setProperty(self, key, value):
+        if key == 'read':
+            value, param = value.split('.')
+            match = INDEX.match(param)
+            if match:
+                self._param, i = match.groups()
+                self._index = int(i)
+            else:
+                self._param = param
+        super().setProperty(key, value)
+
+    def checkProperties(self):
+        self.applyMainUnit(self.unit)
+        if self._param == self.name:
+            raise ConfigError('illegal recursive read module')
+        super().checkProperties()
+
+    def read_value(self):
+        par = getattr(self.read, self._param)
+        if self._index is None:
+            return par
+        return par[self._index]
+
+    def read_status(self):
+        return IDLE, ''