bpo-39957: Change Signature.parameters to OrderedDict (GH-18988)

Lib/inspect.py

@@ -2733,7 +2733,7 @@ class Signature:
 
  A Signature object has the following public attributes and methods:
 
- * parameters : dict
+ * parameters : OrderedDict
  An ordered mapping of parameters' names to the corresponding
  Parameter objects (keyword-only arguments are in the same order
  as listed in `code.co_varnames`).
@@ -2763,10 +2763,10 @@ def __init__(self, parameters=None, *, return_annotation=_empty,
  """
 
  if parameters is None:
- params = {}
+ params = OrderedDict()
  else:
  if __validate_parameters__:
- params = {}
+ params = OrderedDict()
  top_kind = _POSITIONAL_ONLY
  kind_defaults = False
 
@@ -2805,7 +2805,7 @@ def __init__(self, parameters=None, *, return_annotation=_empty,
 
  params[name] = param
  else:
- params = {param.name: param for param in parameters}
+ params = OrderedDict((param.name, param) for param in parameters)
 
  self._parameters = types.MappingProxyType(params)
  self._return_annotation = return_annotation

Lib/test/test_inspect.py

@@ -2077,7 +2077,7 @@ def test_signature_object(self):
  P = inspect.Parameter
 
  self.assertEqual(str(S()), '()')
- self.assertEqual(repr(S().parameters), 'mappingproxy({})')
+ self.assertEqual(repr(S().parameters), 'mappingproxy(OrderedDict())')
 
  def test(po, pk, pod=42, pkd=100, *args, ko, **kwargs):
  pass
@@ -3181,6 +3181,11 @@ def test_signature_definition_order_preserved_on_kwonly(self):
  l = list(signature.parameters)
  self.assertEqual(l, unsorted_keyword_only_parameters)
 
+ def test_signater_parameters_is_ordered(self):
+ p1 = inspect.signature(lambda x, y: None).parameters
+ p2 = inspect.signature(lambda y, x: None).parameters
+ self.assertNotEqual(p1, p2)
+
 
 class TestParameterObject(unittest.TestCase):
  def test_signature_parameter_kinds(self):