Add a convenience func to retrieve the internal attr. hist.

A new function that can be imported to read the internal attribute history. The history is conveniently converted to a numpy.array.

What is missing: I could also extract the time stamps but did not know how to add that to the retrieved array. Could be done later.

lib/get_internal_attribute_history.py

@@ -9,7 +9,7 @@ def get_internal_attribute_history(device: DeviceProxy, attribute_name: str, dep
     try:
         history = array(device.attribute_history(attr_name = attribute_name, depth = depth))
     except Exception as e:
-        raise ValueError("An exception was raised when attempting to access the internal history of the attribute '{}/{}'.".format(device.name(), attribute_name)) from e
+        raise ValueError("Cannot access the internal history of the attribute '{}/{}'.".format(device.name(), attribute_name)) from e
 
     history_values = array([entry.value for entry in history])
     history_values_transposed = history_values.transpose()