Implement __gt__ method on FeatureColumn base class so that they are sortable in Python 3.

PiperOrigin-RevId: 259409662

tensorflow/python/feature_column/feature_column.py

@@ -1758,12 +1758,15 @@ class _FeatureColumn(object):
     pass
 
   def __lt__(self, other):
-    """Allows feature columns to be sortable in Python 3 as they are in 2.
+    """Allows feature columns to be sorted in Python 3 as they are in Python 2.
 
     Feature columns need to occasionally be sortable, for example when used as
     keys in a features dictionary passed to a layer.
 
-    `__lt__` is the only method needed for sorting in CPython:
+    In CPython, `__lt__` must be defined for all objects in the
+    sequence being sorted. If any objects do not have an `__lt__` compatible
+    with feature column objects (such as strings), then CPython will fall back
+    to using the `__gt__` method below.
     https://docs.python.org/3/library/stdtypes.html#list.sort
 
     Args:
@@ -1772,10 +1775,30 @@ class _FeatureColumn(object):
     Returns:
       True if the string representation of this object is lexicographically less
       than the string representation of `other`. For FeatureColumn objects,
-      this looks like "<__main__.FeatureColumn object at 0x7fa1fc02bba8>".
+      this looks like "<__main__.FeatureColumn object at 0xa>".
     """
     return str(self) < str(other)
 
+  def __gt__(self, other):
+    """Allows feature columns to be sorted in Python 3 as they are in Python 2.
+
+    Feature columns need to occasionally be sortable, for example when used as
+    keys in a features dictionary passed to a layer.
+
+    `__gt__` is called when the "other" object being compared during the sort
+    does not have `__lt__` defined.
+    Example: http://gpaste/4803354716798976
+
+    Args:
+      other: The other object to compare to.
+
+    Returns:
+      True if the string representation of this object is lexicographically
+      greater than the string representation of `other`. For FeatureColumn
+      objects, this looks like "<__main__.FeatureColumn object at 0xa>".
+    """
+    return str(self) > str(other)
+
   @property
   def _var_scope_name(self):
     """Returns string. Used for variable_scope. Defaults to self.name."""

tensorflow/python/feature_column/feature_column_v2.py

@@ -2198,12 +2198,17 @@ class FeatureColumn(object):
     pass
 
   def __lt__(self, other):
-    """Allows feature columns to be sortable in Python 3 as they are in 2.
+    """Allows feature columns to be sorted in Python 3 as they are in Python 2.
 
     Feature columns need to occasionally be sortable, for example when used as
     keys in a features dictionary passed to a layer.
 
-    `__lt__` is the only method needed for sorting in CPython:
+    In CPython, `__lt__` must be defined for all objects in the
+    sequence being sorted.
+
+    If any objects in teh sequence being sorted do not have an `__lt__` method
+    compatible with feature column objects (such as strings), then CPython will
+    fall back to using the `__gt__` method below.
     https://docs.python.org/3/library/stdtypes.html#list.sort
 
     Args:
@@ -2212,10 +2217,30 @@ class FeatureColumn(object):
     Returns:
       True if the string representation of this object is lexicographically less
       than the string representation of `other`. For FeatureColumn objects,
-      this looks like "<__main__.FeatureColumn object at 0x7fa1fc02bba8>".
+      this looks like "<__main__.FeatureColumn object at 0xa>".
     """
     return str(self) < str(other)
 
+  def __gt__(self, other):
+    """Allows feature columns to be sorted in Python 3 as they are in Python 2.
+
+    Feature columns need to occasionally be sortable, for example when used as
+    keys in a features dictionary passed to a layer.
+
+    `__gt__` is called when the "other" object being compared during the sort
+    does not have `__lt__` defined.
+    Example: http://gpaste/4803354716798976
+
+    Args:
+      other: The other object to compare to.
+
+    Returns:
+      True if the string representation of this object is lexicographically
+      greater than the string representation of `other`. For FeatureColumn
+      objects, this looks like "<__main__.FeatureColumn object at 0xa>".
+    """
+    return str(self) > str(other)
+
   @abc.abstractmethod
   def transform_feature(self, transformation_cache, state_manager):
     """Returns intermediate representation (usually a `Tensor`).

tensorflow/python/feature_column/feature_column_v2_test.py

@@ -99,7 +99,7 @@ class SortableFeatureColumnTest(test.TestCase):
     a = fc.numeric_column('first')  # '<__main__.NumericColumn object at 0xa>'
     b = fc.numeric_column('second')  # '<__main__.NumericColumn object at 0xb>'
     c = fc_old._numeric_column('third')  # '<__main__._NumericColumn ...>'
-    self.assertAllEqual(sorted(['d', c, b, a]), [a, b, c, 'd'])
+    self.assertAllEqual(sorted(['d', c, b, a, '0']), ['0', a, b, c, 'd'])
 
 
 class LazyColumnTest(test.TestCase):