columns: Make 'FormattableColumn' comparable

Currently, comparing instances of this fails:

  >>> from cliff.columns import FormattableColumn
  >>> class Test(FormattableColumn):
  ...     def human_readable(self):
  ...         return str(self._data)
  ...
  >>> data = {'x': 'y'}
  >>> x = Test(data)
  >>> y = Test(data)
  >>> x == y
  False

Clearly it should not. Resolve this by implementing a custom comparison.

Change-Id: I4b96475ca6a689f4055dc5ea34b82b3867a65555
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>
Story: #2008320
Task: #41218

cliff/columns.py

@@ -24,17 +24,20 @@ class FormattableColumn(object):
     def __init__(self, value):
         self._value = value
 
+    def __eq__(self, other):
+        return (
+            self.__class__ == other.__class__ and self._value == other._value
+        )
+
     @abc.abstractmethod
     def human_readable(self):
-        """Return a basic human readable version of the data.
-        """
+        """Return a basic human readable version of the data."""
 
     def machine_readable(self):
         """Return a raw data structure using only Python built-in types.
 
         It must be possible to serialize the return value directly
         using a formatter like JSON, and it will be up to the
         formatter plugin to decide how to make that transformation.
-
         """
         return self._value