Add a 'keep' parameter to the function CopyFieldsTo in hyperparams.py

PiperOrigin-RevId: 490126504

Author: tonybruguier

lingvo/core/hyperparams.py

@@ -210,6 +210,35 @@ def CopyFieldsTo(from_p, to_p, skip=None, ignore_unknown_keys=False):
   return to_p
 
 
+def CopyFieldsSubsetTo(from_p, to_p, fields_to_set):
+  """Copy fields from one Params to another, with optional skipped params.
+
+  Preserves `type(to_p.Instantiate())`. Use `from_p.Copy()` instead if requiring
+  a deep copy of `from_p`, without updating `to_p`.
+
+  Args:
+    from_p: Source params to copy from.
+    to_p: Destination params to copy to.
+    fields_to_set: A string, a list of strings or None. Params to copy.
+
+  Returns:
+    The updated to_p.
+  """
+  if not isinstance(fields_to_set, list):
+    fields_to_set = [fields_to_set]
+
+  for key, value in from_p.IterParams():
+    if key == 'cls':
+      continue
+    if key not in fields_to_set:
+      continue
+    if isinstance(value, Params):
+      to_p.Set(**{key: value.Copy()})
+    else:
+      to_p.Set(**{key: value})
+  return to_p
+
+
 ParamsT = TypeVar('ParamsT', bound='Params')
 
 

lingvo/core/hyperparams_test.py

@@ -166,6 +166,20 @@ def testCopyFieldsToDoesNotCopyClass(self):
     hyperparams.CopyFieldsTo(source, dest)
     self.assertEqual(dest.cls, hyperparams.InstantiableParams)
 
+  def testCopyFieldsSubsetTo(self):
+    source = hyperparams.Params()
+    dest = hyperparams.Params()
+    source.Define('a', 'a', '')
+    source.Define('b', 'b', '')
+    source.Define('c', 'c', '')
+    dest.Define('a', '', '')
+    dest.Define('d', 'd', '')
+    hyperparams.CopyFieldsSubsetTo(source, dest, ['a'])
+    self.assertEqual(source.a, dest.a)
+    self.assertNotIn('b', dest)
+    self.assertNotIn('c', dest)
+    self.assertEqual(dest.d, 'd')
+
   def testDefineExisting(self):
     p = hyperparams.Params()
     p.Define('foo', 1, '')