bpo-33461: emit DeprecationWarning when json.loads(encoding=...) is used (GH-6762)

2 files changed, 15 insertions, 2 deletions

diff --git a/Lib/json/__init__.py b/Lib/json/__init__.py
index 3bb4490..1ba8b48 100644
--- a/Lib/json/__init__.py
+++ b/Lib/json/__init__.py
@@ -296,7 +296,7 @@ def load(fp, *, cls=None, object_hook=None, parse_float=None,
         parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
 
 
-def loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None,
+def loads(s, *, cls=None, object_hook=None, parse_float=None,
         parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):
     """Deserialize ``s`` (a ``str``, ``bytes`` or ``bytearray`` instance
     containing a JSON document) to a Python object.
@@ -330,7 +330,7 @@ def loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None,
     To use a custom ``JSONDecoder`` subclass, specify it with the ``cls``
     kwarg; otherwise ``JSONDecoder`` is used.
 
-    The ``encoding`` argument is ignored and deprecated.
+    The ``encoding`` argument is ignored and deprecated since Python 3.1.
     """
     if isinstance(s, str):
         if s.startswith('\ufeff'):
@@ -342,6 +342,15 @@ def loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None,
                             f'not {s.__class__.__name__}')
         s = s.decode(detect_encoding(s), 'surrogatepass')
 
+    if "encoding" in kw:
+        import warnings
+        warnings.warn(
+            "'encoding' is ignored and deprecated. It will be removed in Python 3.9",
+            DeprecationWarning,
+            stacklevel=2
+        )
+        del kw['encoding']
+
     if (cls is None and object_hook is None and
             parse_int is None and parse_float is None and
             parse_constant is None and object_pairs_hook is None and not kw):
diff --git a/Lib/test/test_json/test_decode.py b/Lib/test/test_json/test_decode.py
index fdb9e62..895c95b 100644
--- a/Lib/test/test_json/test_decode.py
+++ b/Lib/test/test_json/test_decode.py
@@ -95,5 +95,9 @@ class TestDecode:
         d = self.json.JSONDecoder()
         self.assertRaises(ValueError, d.raw_decode, 'a'*42, -50000)
 
+    def test_deprecated_encode(self):
+        with self.assertWarns(DeprecationWarning):
+            self.loads('{}', encoding='fake')
+
 class TestPyDecode(TestDecode, PyTest): pass
 class TestCDecode(TestDecode, CTest): pass