Apply TR fixes

Author: bzaczynski

python-mixins/typed_dict.py

@@ -0,0 +1,59 @@
+def typed_dict(key_type=object, value_type=object):
+    def class_decorator(cls):
+        setitem = cls.__setitem__
+
+        def __setitem__(self, key, value):
+            if not isinstance(key, key_type):
+                raise TypeError(
+                    f"value must be {key_type} but was {type(key)}"
+                )
+
+            if not isinstance(value, value_type):
+                raise TypeError(
+                    f"value must be {value_type} but was {type(value)}"
+                )
+
+            setitem(self, key, value)
+
+        cls.__setitem__ = __setitem__
+
+        return cls
+
+    return class_decorator
+
+
+if __name__ == "__main__":
+    from collections import UserDict
+
+    # Enforce str keys and int values:
+    @typed_dict(str, int)
+    class Inventory(UserDict):
+        pass
+
+    # Enforce str keys, allow any value type:
+    @typed_dict(str)
+    class AppSettings(UserDict):
+        pass
+
+    fruits = Inventory()
+    fruits["apples"] = 42
+
+    try:
+        fruits["🍌".encode("utf-8")] = 15
+    except TypeError as ex:
+        print(ex)
+
+    try:
+        fruits["bananas"] = 3.5
+    except TypeError as ex:
+        print(ex)
+
+    settings = AppSettings()
+    settings["host"] = "localhost"
+    settings["port"] = 8080
+    settings["debug_mode"] = True
+
+    try:
+        settings[b"binary data"] = "nope"
+    except TypeError as ex:
+        print(ex)