Add an initial set of type hints

These focus on the public API with the private aspect omitted. This is
because these are hard to type, and may not be required with modern
python. However, this should still be useful if adopted for code
that uses blinker.

MANIFEST.in

@@ -1,5 +1,6 @@
 include CHANGES.rst
 include tox.ini
+include src/blinker/py.typed
 graft docs
 prune docs/_build
 graft tests

pyproject.toml

@@ -24,6 +24,7 @@ classifiers = [
 ]
 requires-python = ">= 3.7"
 dynamic = ["version"]
+dependencies = ["typing-extensions"]
 
 [project.urls]
 Homepage = "https://blinker.readthedocs.io"
@@ -36,6 +37,27 @@ Chat = "https://discord.gg/pallets"
 file = "README.rst"
 content-type = "text/x-rst"
 
+[tool.mypy]
+python_version = "3.7"
+files = ["src/blinker"]
+show_error_codes = true
+pretty = true
+#strict = true
+allow_redefinition = true
+disallow_subclassing_any = true
+#disallow_untyped_calls = true
+#disallow_untyped_defs = true
+disallow_incomplete_defs = true
+no_implicit_optional = true
+local_partial_types = true
+no_implicit_reexport = true
+strict_equality = true
+warn_redundant_casts = true
+warn_unused_configs = true
+warn_unused_ignores = true
+warn_return_any = true
+#warn_unreachable = True
+
 [tool.setuptools]
 license-files = ["LICENSE.rst"]
 include-package-data = false

requirements/typing.in

@@ -0,0 +1 @@
+mypy

requirements/typing.txt

@@ -0,0 +1,13 @@
+# SHA1:7983aaa01d64547827c20395d77e248c41b2572f
+#
+# This file is autogenerated by pip-compile-multi
+# To update, run:
+#
+#    pip-compile-multi
+#
+mypy==1.0.1
+    # via -r requirements/typing.in
+mypy-extensions==1.0.0
+    # via mypy
+typing-extensions==4.5.0
+    # via mypy

src/blinker/_saferef.py

@@ -108,7 +108,7 @@ class BoundMethodWeakref:
       produce the same BoundMethodWeakref instance.
     """
 
-    _all_instances = weakref.WeakValueDictionary()
+    _all_instances = weakref.WeakValueDictionary()  # type: ignore
 
     def __new__(cls, target, on_delete=None, *arguments, **named):
         """Create new instance or return current instance.

src/blinker/_utilities.py

@@ -1,12 +1,14 @@
 import asyncio
 import inspect
 import sys
+import typing as t
 from functools import partial
-from typing import Any
 from weakref import ref
 
 from blinker._saferef import BoundMethodWeakref
 
+IdentityType = t.Union[t.Tuple[int, int], str, int]
+
 
 class _symbol:
     def __init__(self, name):
@@ -38,7 +40,7 @@ class symbol:
 
     """
 
-    symbols = {}
+    symbols = {}  # type: ignore
 
     def __new__(cls, name):
         try:
@@ -47,11 +49,11 @@ def __new__(cls, name):
             return cls.symbols.setdefault(name, _symbol(name))
 
 
-def hashable_identity(obj):
+def hashable_identity(obj: object) -> IdentityType:
     if hasattr(obj, "__func__"):
-        return (id(obj.__func__), id(obj.__self__))
+        return (id(obj.__func__), id(obj.__self__))  # type: ignore
     elif hasattr(obj, "im_func"):
-        return (id(obj.im_func), id(obj.im_self))
+        return (id(obj.im_func), id(obj.im_self))  # type: ignore
     elif isinstance(obj, (int, str)):
         return obj
     else:
@@ -64,16 +66,21 @@ def hashable_identity(obj):
 class annotatable_weakref(ref):
     """A weakref.ref that supports custom instance attributes."""
 
+    receiver_id: t.Optional[IdentityType]
+    sender_id: t.Optional[IdentityType]
+
 
-def reference(object, callback=None, **annotations):
+def reference(  # type: ignore
+    object, callback=None, **annotations
+) -> annotatable_weakref:
     """Return an annotated weak ref."""
     if callable(object):
         weak = callable_reference(object, callback)
     else:
         weak = annotatable_weakref(object, callback)
     for key, value in annotations.items():
         setattr(weak, key, value)
-    return weak
+    return weak  # type: ignore
 
 
 def callable_reference(object, callback=None):
@@ -100,7 +107,7 @@ def __get__(self, obj, cls):
         return value
 
 
-def is_coroutine_function(func: Any) -> bool:
+def is_coroutine_function(func: t.Any) -> bool:
     # Python < 3.8 does not correctly determine partially wrapped
     # coroutine functions are coroutine functions, hence the need for
     # this to exist. Code taken from CPython.
@@ -111,7 +118,7 @@ def is_coroutine_function(func: Any) -> bool:
         # such that it isn't determined as a coroutine function
         # without an explicit check.
         try:
-            from unittest.mock import AsyncMock
+            from unittest.mock import AsyncMock  # type: ignore
 
             if isinstance(func, AsyncMock):
                 return True
@@ -128,5 +135,5 @@ def is_coroutine_function(func: Any) -> bool:
         result = bool(func.__code__.co_flags & inspect.CO_COROUTINE)
         return (
             result
-            or getattr(func, "_is_coroutine", None) is asyncio.coroutines._is_coroutine
+            or getattr(func, "_is_coroutine", None) is asyncio.coroutines._is_coroutine  # type: ignore  # noqa: B950
         )