Add hints for most of the basic challenges & improved basic-optional (#72)

Author: piglei

challenges/basic-dict/hints.md

@@ -0,0 +1 @@
+Check out [Dict](https://docs.python.org/3/library/typing.html#typing.Dict) or use the built-in `dict` function, the syntax for using `dict` for typing looks like this: `dict[KT, VT]`.

challenges/basic-final/hints.md

@@ -0,0 +1 @@
+Check out [Final](https://docs.python.org/3/library/typing.html#typing.Final).

challenges/basic-list/hints.md

@@ -0,0 +1 @@
+Check out [List](https://docs.python.org/3/library/typing.html#typing.List) or use the built-in `list` function, the syntax for using `list` for typing looks like this: `list[T]`.

challenges/basic-optional/hints.md

@@ -0,0 +1,3 @@
+- A union type can be created using the `|` operator, e.g: `X | Y`
+- `None` can be used for typing directly
+- Type hint doesn't simply make an argument "optional", that's the default value's job

challenges/basic-optional/question.py

@@ -1,7 +1,7 @@
 """
 TODO:
 
-foo can accept either an integer argument or no argument.
+foo can accept an integer argument, None or no argument at all.
 """
 
 
@@ -11,6 +11,7 @@ def foo(x):
 
 ## End of your code ##
 foo(10)
+foo(None)
 foo()
 
 foo("10")  # expect-type-error

challenges/basic-optional/solution.py

@@ -4,6 +4,7 @@ def foo(x: int | None = 0):
 
 ## End of your code ##
 foo(10)
+foo(None)
 foo()
 
 foo("10")  # expect-type-error

challenges/basic-parameter/hints.md

@@ -0,0 +1 @@
+The syntax for adding type hints to an argument is: `foo(x: T)`, replace `T` with the real type.

challenges/basic-return/hints.md

@@ -0,0 +1 @@
+The syntax for adding type hints to a return value is: `foo() -> T`, replace `T` with the real type.

challenges/basic-tuple/hints.md

@@ -0,0 +1 @@
+Check out [Tuple](https://docs.python.org/3/library/typing.html#typing.Tuple).

challenges/basic-typealias/hints.md

@@ -0,0 +1 @@
+Check out [TypeAlias](https://docs.python.org/3/library/typing.html#typing.TypeAlias).