Add generic3 that exercises bound

Author: laike9m

challenges/intermediate-generic2/question.py

@@ -2,7 +2,7 @@
 TODO:
 
 The function `add` accepts two arguments and returns a value, they all have the same type.
-The type can only be str or int.
+The type can only be str or int (or their subclasses).
 """
 
 

challenges/intermediate-generic2/solution.py

@@ -2,7 +2,7 @@
 TODO:
 
 The function `add` accepts two arguments and returns a value, they all have the same type.
-The type can only be str or int.
+The type can only be str or int (or their subclasses).
 """
 from typing import TypeVar
 

challenges/intermediate-generic3/hints.md

@@ -0,0 +1 @@
+[TypeVar](https://docs.python.org/3/library/typing.html#typing.TypeVar) accepts a `bound` argument

challenges/intermediate-generic3/question.py

@@ -0,0 +1,25 @@
+"""
+TODO:
+
+The function `add` accepts one argument and returns a value, they all have the same type.
+The type can only be int or subclasses of int.
+"""
+
+
+def add(a):
+    return a
+
+
+## End of your code ##
+from typing import assert_type
+
+
+class MyInt(int):
+    pass
+
+
+assert_type(add(1), int)
+assert_type(add(MyInt(1)), MyInt)
+assert_type(add("1"), str)  # expect-type-error
+add(["1"], ["2"])  # expect-type-error
+add("1", 2)  # expect-type-error

challenges/intermediate-generic3/solution.py

@@ -0,0 +1,32 @@
+"""
+TODO:
+
+The function `add` accepts one argument and returns a value, they all have the same type.
+The type can only be int or subclasses of int.
+"""
+from typing import TypeVar
+
+T = TypeVar("T", bound=int)
+
+
+def add(a: T) -> T:
+    return a
+
+
+# For Python >= 3.12
+# def add[T: int](a: T) -> T:
+#     return a
+
+## End of your code ##
+from typing import assert_type
+
+
+class MyInt(int):
+    pass
+
+
+assert_type(add(1), int)
+assert_type(add(MyInt(1)), MyInt)
+assert_type(add("1"), str)  # expect-type-error
+add(["1"], ["2"])  # expect-type-error
+add("1", 2)  # expect-type-error