Use DeviceProxy instead of taurus in MacroServer

Use DeviceProxy instead of taurus to avoid crashes in Py3
See: tango-controls/pytango#292

To be reverted when the above issue gets clarified

src/sardana/macroserver/scan/gscan.py

@@ -666,7 +666,10 @@ def _setupEnvironment(self, additional_env):
         for ci in channels_info:
             full_name = ci.full_name
             try:
-                channel = taurus.Device(full_name)
+                # Use DeviceProxy instead of taurus to avoid crashes in Py3
+                # See: tango-controls/pytango#292
+                # channel = taurus.Device(full_name)
+                channel = PyTango.DeviceProxy(full_name)
                 instrument = channel.instrument
             except Exception:
                 # full_name of external channels is the name of the attribute
@@ -2036,7 +2039,10 @@ def is_measurement_group_compatible(measurement_group):
             full_name = channel_info["full_name"]
             name = channel_info["name"]
             try:
-                taurus.Device(full_name)
+                # Use DeviceProxy instead of taurus to avoid crashes in Py3
+                # See: tango-controls/pytango#292
+                # taurus.Device(full_name)
+                PyTango.DeviceProxy(full_name)
             except Exception:
                 # external channels are attributes so Device constructor fails
                 non_compatible_channels.append(name)

src/sardana/taurus/core/tango/sardana/pool.py

@@ -92,6 +92,15 @@
 }
 
 
+def _is_referable(channel):
+    # Equivalent to ExpChannel.isReferable.
+    # Use DeviceProxy instead of taurus to avoid crashes in Py3
+    # See: tango-controls/pytango#292
+    if isinstance(channel, str):
+        channel = DeviceProxy(channel)
+    return "valueref" in list(map(str.lower, channel.get_attribute_list()))
+
+
 class InterruptException(Exception):
     pass
 
@@ -1447,12 +1456,15 @@ def _build(self):
                 dev_data = tg_dev_chs.get(dev_name)
                 # technical debt: read Value or ValueRef attribute
                 # ideally the source configuration should include this info
-                channel = Device(dev_name)
-                if (isinstance(channel, ExpChannel)
-                        and channel.isReferable()
+                # Use DeviceProxy instead of taurus to avoid crashes in Py3
+                # See: tango-controls/pytango#292
+                # channel = Device(dev_name)
+                # if (isinstance(channel, ExpChannel)
+                #         and channel.isReferable()
+                #         and channel_data.get("value_ref_enabled", False)):
+                if (_is_referable(dev_name)
                         and channel_data.get("value_ref_enabled", False)):
                     attr_name += "Ref"
-
                 if dev_data is None:
                     # Build tango device
                     dev = None
@@ -1898,9 +1910,11 @@ def subscribeValueBuffer(self, cb=None):
         for channel_info in self.getChannels():
             full_name = channel_info["full_name"]
             value_ref_enabled = channel_info.get("value_ref_enabled", False)
-            channel = Device(full_name)
-            if channel.isReferable() and value_ref_enabled:
+            # Use DeviceProxy instead of taurus to avoid crashes in Py3
+            # See: tango-controls/pytango#292
+            if _is_referable(full_name) and value_ref_enabled:
                 continue
+            channel = Device(full_name)
             value_buffer_obj = channel.getValueBufferObj()
             if cb is not None:
                 self._value_buffer_cb = cb
@@ -1922,9 +1936,11 @@ def unsubscribeValueBuffer(self, cb=None):
         for channel_info in self.getChannels():
             full_name = channel_info["full_name"]
             value_ref_enabled = channel_info.get("value_ref_enabled", False)
-            channel = Device(full_name)
-            if channel.isReferable() and value_ref_enabled:
+            # Use DeviceProxy instead of taurus to avoid crashes in Py3
+            # See: tango-controls/pytango#292
+            if _is_referable(full_name) and value_ref_enabled:
                 continue
+            channel = Device(full_name)
             value_buffer_obj = channel.getValueBufferObj()
             if cb is not None:
                 value_buffer_obj.unsubscribeEvent(self.valueBufferChanged,
@@ -1963,11 +1979,13 @@ def subscribeValueRefBuffer(self, cb=None):
         for channel_info in self.getChannels():
             full_name = channel_info["full_name"]
             value_ref_enabled = channel_info.get("value_ref_enabled", False)
-            channel = Device(full_name)
-            if not channel.isReferable():
+            # Use DeviceProxy instead of taurus to avoid crashes in Py3
+            # See: tango-controls/pytango#292
+            if not _is_referable(full_name):
                 continue
             if not value_ref_enabled:
                 continue
+            channel = Device(full_name)
             value_ref_buffer_obj = channel.getValueRefBufferObj()
             if cb is not None:
                 self._value_ref_buffer_cb = cb
@@ -1989,11 +2007,13 @@ def unsubscribeValueRefBuffer(self, cb=None):
         for channel_info in self.getChannels():
             full_name = channel_info["full_name"]
             value_ref_enabled = channel_info.get("value_ref_enabled", False)
-            channel = Device(full_name)
-            if not channel.isReferable():
+            # Use DeviceProxy instead of taurus to avoid crashes in Py3
+            # See: tango-controls/pytango#292
+            if not _is_referable(full_name):
                 continue
             if not value_ref_enabled:
                 continue
+            channel = Device(full_name)
             value_ref_buffer_obj = channel.getValueRefBufferObj()
             if cb is not None:
                 value_ref_buffer_obj.unsubscribeEvent(