Add a challenge about variance

Author: laike9m

challenges/extreme-variance/question.py

@@ -0,0 +1,22 @@
+"""
+Annotate function `f` and `g`, to make tests pass.
+"""
+
+
+def f(a):
+    pass
+
+
+def g(a):
+    pass
+
+
+## End of your code ##
+
+l1: list[int] = [1, 2]
+f(l1)  # expect-type-error
+g(l1)
+
+l2: list[int | str] = [1, 2]
+f(l2)
+g(l2)

challenges/extreme-variance/solution.py

@@ -0,0 +1,24 @@
+"""
+Annotate function `f` and `g`, to make tests pass.
+"""
+
+from collections.abc import Sequence
+
+
+def f(a: list[int | str]):
+    pass
+
+
+def g(a: Sequence[int | str]):
+    pass
+
+
+## End of your code ##
+
+l1: list[int] = [1, 2]
+f(l1)  # expect-type-error
+g(l1)
+
+l2: list[int | str] = [1, 2]
+f(l2)
+g(l2)