Preserve cause of exception when getting/setting attribute in DeviceProxy

setup.py

@@ -486,16 +486,21 @@ def setup_args():
         setup_requires += ['pytest-runner']
 
     tests_require = [
-        'pytest-xdist',
         'gevent != 1.5a1',
         'psutil',
     ]
 
     if PYTHON2:
         tests_require += [
-            'trollius', 'futures', 'pyparsing < 3', 'pytest < 5', 'zipp >= 0.5, < 2']
+            'futures',
+            'pyparsing < 3',
+            'pytest < 5',
+            'pytest-xdist < 2',
+            'trollius',
+            'zipp >= 0.5, < 2',
+        ]
     else:
-        tests_require += ['pytest']
+        tests_require += ['pytest', 'pytest-xdist']
 
     package_data = {
         'tango.databaseds': ['*.xmi', '*.sql', '*.sh', 'DataBaseds'],

tango/device_proxy.py

@@ -272,11 +272,12 @@ def __set_attribute_value(self, name, value):
 
 
 def __DeviceProxy__getattr(self, name):
+    cause = None
     # trait_names is a feature of IPython. Hopefully they will solve
     # ticket http://ipython.scipy.org/ipython/ipython/ticket/229 someday
     # and the ugly trait_names could be removed.
     if name.startswith("_") or name == 'trait_names':
-        raise AttributeError(name)
+        six.raise_from(AttributeError(name), cause)
 
     name_l = name.lower()
 
@@ -293,38 +294,42 @@ def __DeviceProxy__getattr(self, name):
 
     try:
         self.__refresh_cmd_cache()
-    except:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     cmd_info = self.__get_cmd_cache().get(name_l)
     if cmd_info:
         return __get_command_func(self, cmd_info, name)
 
     try:
         self.__refresh_attr_cache()
-    except:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     attr_info = self.__get_attr_cache().get(name_l)
     if attr_info:
         return __get_attribute_value(self, attr_info, name)
 
     try:
         self.__refresh_pipe_cache()
-    except Exception:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     if name_l in self.__get_pipe_cache():
         return self.read_pipe(name)
 
-    raise AttributeError(name)
+    six.raise_from(AttributeError(name), cause)
 
 
 def __DeviceProxy__setattr(self, name, value):
+    cause = None
     name_l = name.lower()
 
     if name_l in self.__get_cmd_cache():
-        raise TypeError('Cannot set the value of a command')
+        six.raise_from(TypeError('Cannot set the value of a command'), cause)
 
     if name_l in self.__get_attr_cache():
         return __set_attribute_value(self, name, value)
@@ -334,29 +339,35 @@ def __DeviceProxy__setattr(self, name, value):
 
     try:
         self.__refresh_cmd_cache()
-    except:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     if name_l in self.__get_cmd_cache():
-        raise TypeError('Cannot set the value of a command')
+        six.raise_from(TypeError('Cannot set the value of a command'), cause)
 
     try:
         self.__refresh_attr_cache()
-    except:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     if name_l in self.__get_attr_cache():
         return __set_attribute_value(self, name, value)
 
     try:
         self.__refresh_pipe_cache()
-    except:
-        pass
+    except Exception as e:
+        if cause is None:
+            cause = e
 
     if name_l in self.__get_pipe_cache():
         return self.write_pipe(name, value)
 
-    return super(DeviceProxy, self).__setattr__(name, value)
+    try:
+        return super(DeviceProxy, self).__setattr__(name, value)
+    except Exception as e:
+        six.raise_from(e, cause)
 
 
 def __DeviceProxy__dir(self):