From 70c40f70d043f0b39386a8aadf3a8d6a4cb55c64 Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Mon, 2 Aug 2021 12:58:53 +0300
Subject: [PATCH] bpo-44807: Forbid to define __init__ method in Protocol
 classes

---
 Lib/test/test_typing.py                                    | 7 +++++++
 Lib/typing.py                                              | 4 ++++
 .../next/Library/2021-08-02-12-58-14.bpo-44807.UvHEKh.rst  | 2 ++
 3 files changed, 13 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2021-08-02-12-58-14.bpo-44807.UvHEKh.rst

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 6cd83a1586a136..0b811ac3e44bd3 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -1558,6 +1558,13 @@ class P(Protocol):
         with self.assertRaisesRegex(TypeError, "@runtime_checkable"):
             isinstance(1, P)
 
+    def test_protocol_init_is_forbidden(self): # see bpo-44807
+        with self.assertRaisesRegex(TypeError, 'Protocols can not have __init__ method'):
+            class P(Protocol):
+                x: int
+
+                def __init__(self, x: int):
+                    self.x = x
 
 class GenericTests(BaseTestCase):
 
diff --git a/Lib/typing.py b/Lib/typing.py
index 16ad5ce7c2d04b..e481ce24444ac6 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1532,6 +1532,10 @@ def _proto_hook(other):
                     issubclass(base, Generic) and base._is_protocol):
                 raise TypeError('Protocols can only inherit from other'
                                 ' protocols, got %r' % base)
+
+        if '__init__' in cls.__dict__:
+            raise TypeError('Protocols can not have __init__ method')
+
         cls.__init__ = _no_init
 
 
diff --git a/Misc/NEWS.d/next/Library/2021-08-02-12-58-14.bpo-44807.UvHEKh.rst b/Misc/NEWS.d/next/Library/2021-08-02-12-58-14.bpo-44807.UvHEKh.rst
new file mode 100644
index 00000000000000..19015dc4573822
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-08-02-12-58-14.bpo-44807.UvHEKh.rst
@@ -0,0 +1,2 @@
+Forbid to define ``__init__`` method in ``Protocol`` classes. Patch provided
+by Yurii Karabas.